net: amt: Remove generic .ndo_get_stats64

Commit 3e2f544dd8a33 ("net: get stats64 if device if driver is
configured") moved the callback to dev_get_tstats64() to net core, so,
unless the driver is doing some custom stats collection, it does not
need to set .ndo_get_stats64.

Since this driver is now relying in NETDEV_PCPU_STAT_TSTATS, then, it
doesn't need to set the dev_get_tstats64() generic .ndo_get_stats64
function pointer.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20240308162606.1597287-2-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: amt: Move stats allocation to core

With commit 34d21de99cea9 ("net: Move {l,t,d}stats allocation to core and
convert veth & vrf"), stats allocation could be done on net core instead
of this driver.

With this new approach, the driver doesn't have to bother with error
handling (allocation failure checking, making sure free happens in the
right spot, etc). This is core responsibility now.

Move amt driver to leverage the core allocation.

Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20240308162606.1597287-1-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: do not use overwrapped cb area

amt driver uses skb->cb for storing tunnel information.
This job is worked before TC layer and then amt driver load tunnel info
from skb->cb after TC layer.
So, its cb area should not be overwrapped with CB area used by TC.
In order to not use cb area used by TC, it skips the biggest cb
structure used by TC, which was qdisc_skb_cb.
But it's not anymore.
Currently, biggest structure of TC's CB is tc_skb_cb.
So, it should skip size of tc_skb_cb instead of qdisc_skb_cb.

Fixes: ec624fe740b4 ("net/sched: Extend qdisc control block with tc control block")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20240107144241.4169520-1-ap420073@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: fill in MODULE_DESCRIPTION()s under drivers/net/

W=1 builds now warn if module is built without a MODULE_DESCRIPTION().

Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: remove unnecessary skb pointer check

The skb pointer will be checked in kfree_skb(), so remove the outside check.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20220818093114.2449179-1-yangyingliang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix typo in comment

Correct spelling on 'non-existent' in comment

Signed-off-by: Ruffalo Lavoisier <RuffaloLavoisier@gmail.com>
Link: https://lore.kernel.org/r/20220728032854.151180-1-RuffaloLavoisier@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: remove unnecessary (void*) conversions

Remove unnecessary void* type castings.

Signed-off-by: Yu Zhe <yuzhe@nfschina.com>
Acked-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20220621021648.2544-1-yuzhe@nfschina.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: do not use amt->nr_tunnels outside of lock

amt->nr_tunnels is protected by amt->lock.
But, amt_request_handler() has been using this variable without the
amt->lock.
So, it expands context of amt->lock in the amt_request_handler() to
protect amt->nr_tunnels variable.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: drop unexpected multicast data

AMT gateway interface should not receive unexpected multicast data.
Multicast data message type should be received after sending an update
message, which means all establishment between gateway and relay is
finished.
So, amt_multicast_data_handler() checks amt->status.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: drop unexpected query message

AMT gateway interface should not receive unexpected query messages.
In order to drop unexpected query messages, it checks nonce.
And it also checks ready4 and ready6 variables to drop duplicated messages.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: drop unexpected advertisement message

AMT gateway interface should not receive unexpected advertisement messages.
In order to drop these packets, it should check nonce and amt->status.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: add missing regeneration nonce logic in request logic

When AMT gateway starts sending a new request message, it should
regenerate the nonce variable.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: use READ_ONCE() in amt module

There are some data races in the amt module.
amt->ready4, amt->ready6, and amt->status can be accessed concurrently
without locks.
So, it uses READ_ONCE() and WRITE_ONCE().

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: remove unnecessary locks

By the previous patch, amt gateway handlers are changed to worked by
a single thread.
So, most locks for gateway are not needed.
So, it removes.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

amt: use workqueue for gateway side message handling

There are some synchronization issues(amt->status, amt->req_cnt, etc)
if the interface is in gateway mode because gateway message handlers
are processed concurrently.
This applies a work queue for processing these messages instead of
expanding the locking context.

So, the purposes of this patch are to fix exist race conditions and to make
gateway to be able to validate a gateway status more correctly.

When the AMT gateway interface is created, it tries to establish to relay.
The establishment step looks stateless, but it should be managed well.
In order to handle messages in the gateway, it saves the current
status(i.e. AMT_STATUS_XXX).
This patch makes gateway code to be worked with a single thread.

Now, all messages except the multicast are triggered(received or
delay expired), and these messages will be stored in the event
queue(amt->events).
Then, the single worker processes stored messages asynchronously one
by one.
The multicast data message type will be still processed immediately.

Now, amt->lock is only needed to access the event queue(amt->events)
if an interface is the gateway mode.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

igmp: Fix data-races around sysctl_igmp_qrv.

While reading sysctl_igmp_qrv, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its readers.

This test can be packed into a helper, so such changes will be in the
follow-up series after net is merged into net-next.

qrv ?: READ_ONCE(net->ipv4.sysctl_igmp_qrv);

Fixes: a9fe8e29945d ("ipv4: implement igmp_qrv sysctl to tune igmp robustness variable")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: fix wrong type string definition

amt message type definition starts from 1, not 0.
But type_str[] starts from 0.
So, it prints wrong type information.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix possible null-ptr-deref in amt_rcv()

When amt interface receives amt message, it tries to obtain amt private
data from sock.
If there is no amt private data, it frees an skb immediately.
After kfree_skb(), it increases the rx_dropped stats.
But in order to use rx_dropped, amt private data is needed.
So, it makes amt_rcv() to do not increase rx_dropped stats when it can
not obtain amt private data.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 1a1a0e80e005 ("amt: fix possible memory leak in amt_rcv()")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix wrong usage of pskb_may_pull()

It adds missing pskb_may_pull() in amt_update_handler() and
amt_multicast_data_handler().
And it fixes wrong parameter of pskb_may_pull() in
amt_advertisement_handler() and amt_membership_query_handler().

Reported-by: Jakub Kicinski <kuba@kernel.org>
Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix possible memory leak in amt_rcv()

If an amt receives packets and it finds socket.
If it can't find a socket, it should free a received skb.
But it doesn't.
So, a memory leak would possibly occur.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix return value of amt_update_handler()

If a relay receives an update message, it lookup a tunnel.
and if there is no tunnel for that message, it should be treated
as an error, not a success.
But amt_update_handler() returns false, which means success.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix typo in amt

AMT_MSG_TEARDOWM is defined,
But it should be AMT_MSG_TEARDOWN.

Fixes: b9022b53adad ("amt: add control plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix memory leak for advertisement message

When a gateway receives an advertisement message, it extracts relay
information and then it should be freed.
But the advertisement handler doesn't free it.
So, memory leak would occur.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: fix gateway mode stuck

If a gateway can not receive any response to requests from a relay,
gateway resets status from SENT_REQUEST to INIT and variable about a
relay as well. And then it should start the full establish step
from sending a discovery message and receiving advertisement message.
But, after failure in amt_req_work() it continues sending a request
message step with flushed(invalid) relay information and sets SENT_REQUEST.
So, a gateway can't be established with a relay.
In order to avoid this situation, it stops sending the request message
step if it fails.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: dev: Makes sure netif_rx() can be invoked in any context.

Dave suggested a while ago (eleven years by now) "Let's make netif_rx()
work in all contexts and get rid of netif_rx_ni()". Eric agreed and
pointed out that modern devices should use netif_receive_skb() to avoid
the overhead.
In the meantime someone added another variant, netif_rx_any_context(),
which behaves as suggested.

netif_rx() must be invoked with disabled bottom halves to ensure that
pending softirqs, which were raised within the function, are handled.
netif_rx_ni() can be invoked only from process context (bottom halves
must be enabled) because the function handles pending softirqs without
checking if bottom halves were disabled or not.
netif_rx_any_context() invokes on the former functions by checking
in_interrupts().

netif_rx() could be taught to handle both cases (disabled and enabled
bottom halves) by simply disabling bottom halves while invoking
netif_rx_internal(). The local_bh_enable() invocation will then invoke
pending softirqs only if the BH-disable counter drops to zero.

Eric is concerned about the overhead of BH-disable+enable especially in
regard to the loopback driver. As critical as this driver is, it will
receive a shortcut to avoid the additional overhead which is not needed.

Add a local_bh_disable() section in netif_rx() to ensure softirqs are
handled if needed.
Provide __netif_rx() which does not disable BH and has a lockdep assert
to ensure that interrupts are disabled. Use this shortcut in the
loopback driver and in drivers/net/*.c.
Make netif_rx_ni() and netif_rx_any_context() invoke netif_rx() so they
can be removed once they are no more users left.

Link: https://lkml.kernel.org/r/20100415.020246.218622820.davem@davemloft.net
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: fix wrong return type of amt_send_membership_update()

amt_send_membership_update() would return -1 but it's return type is bool.
So, it should be used TRUE instead of -1.

Fixes: cbc21dc1cfe9 ("amt: add data plane of amt interface")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20220109163702.6331-1-ap420073@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: Don't include filter.h from net/sock.h

sock.h is pretty heavily used (5k objects rebuilt on x86 after
it's touched). We can drop the include of filter.h from it and
add a forward declaration of struct sk_filter instead.
This decreases the number of rebuilt objects when bpf.h
is touched from ~5k to ~1k.

There's a lot of missing includes this was masking. Primarily
in networking tho, this time.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/bpf/20211229004913.513372-1-kuba@kernel.org

amt: cancel delayed_work synchronously in amt_fini()

When the amt module is being removed, it calls cancel_delayed_work()
to cancel pending delayed_work. But this function doesn't wait for
canceling delayed_work.
So, workers can be still doing after module delete.

In order to avoid this, cancel_delayed_work_sync() should be used instead.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Fixes: bc54e49c140b ("amt: add multicast(IGMP) report message handler")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20211116160923.25258-1-ap420073@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: use cancel_delayed_work() instead of flush_delayed_work() in amt_fini()

When the amt module is being removed, it calls flush_delayed_work() to exit
source_gc_wq. But it wouldn't be exited properly because the
amt_source_gc_work(), which is the callback function of source_gc_wq
internally calls mod_delayed_work() again.
So, amt_source_gc_work() would be called after the amt module is removed.
Therefore kernel panic would occur.
In order to avoid it, cancel_delayed_work() should be used instead of
flush_delayed_work().

Test commands:
modprobe amt
modprobe -rv amt

Splat looks like:
BUG: unable to handle page fault for address: fffffbfff80f50db
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 1237ee067 P4D 1237ee067 PUD 1237b2067 PMD 100c11067 PTE 0
Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC KASAN PTI
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0+ #27
5a0ebebc29fe5c40c68bea90197606c3a832b09f
RIP: 0010:run_timer_softirq+0x221/0xfc0
Code: 00 00 4c 89 e1 4c 8b 30 48 c1 e9 03 80 3c 29 00 0f 85 ed 0b 00 00
4d 89 34 24 4d 85 f6 74 19 49 8d 7e 08 48 89 f9 48 c1 e9 03 <80> 3c 29 00
0f 85 fa 0b 00 00 4d 89 66 08 83 04 24 01 49 89 d4 48
RSP: 0018:ffff888119009e50 EFLAGS: 00010806
RAX: ffff8881191f8a80 RBX: 00000000007ffe2a RCX: 1ffffffff80f50db
RDX: ffff888119009ed0 RSI: 0000000000000008 RDI: ffffffffc07a86d8
RBP: dffffc0000000000 R08: ffff8881191f8280 R09: ffffed102323f061
R10: ffff8881191f8307 R11: ffffed102323f060 R12: ffff888119009ec8
R13: 00000000000000c0 R14: ffffffffc07a86d0 R15: ffff8881191f82e8
FS: 0000000000000000(0000) GS:ffff888119000000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffbfff80f50db CR3: 00000001062dc002 CR4: 00000000003706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
? add_timer+0x650/0x650
? kvm_clock_read+0x14/0x30
? ktime_get+0xb9/0x180
? rcu_read_lock_held_common+0xe/0xa0
? rcu_read_lock_sched_held+0x56/0xc0
? rcu_read_lock_bh_held+0xa0/0xa0
? hrtimer_interrupt+0x271/0x790
__do_softirq+0x1d0/0x88f
irq_exit_rcu+0xe7/0x120
sysvec_apic_timer_interrupt+0x8a/0xb0
</IRQ>
<TASK>
[ ... ]

Fixes: bc54e49c140b ("amt: add multicast(IGMP) report message handler")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20211108145340.17208-1-ap420073@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: remove duplicate include in amt.c

'net/protocol.h' included in 'drivers/net/amt.c' is duplicated.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Zhang Mingyu <zhang.mingyu@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: Fix NULL but dereferenced coccicheck error

Eliminate the following coccicheck warning:
./drivers/net/amt.c:2795:6-9: ERROR: amt is NULL but dereferenced.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: Remove duplicate include

Clean up the following includecheck warning:

./drivers/net/amt.c: net/protocol.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: fix error return code in amt_init()

Return error code when alloc_workqueue()
fails in amt_init().

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Taehee Yoo <ap420073@gmail.com>
Link: https://lore.kernel.org/r/20211102130353.1666999-1-yangyingliang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

amt: add mld report message handler

In the previous patch, igmp report handler was added.
That handler can be used for mld too.
So, it uses that common code to parse mld report message.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: add multicast(IGMP) report message handler

amt 'Relay' interface manages multicast groups(igmp/mld) and sources.
In order to manage, it should have the function to parse igmp/mld
report messages. So, this adds the logic for parsing igmp report messages
and saves them on their own data structure.

struct amt_group_node means one group(igmp/mld).
struct amt_source_node means one source.

The same source can't exist in the same group.
The same group can exist in the same tunnel because it manages
the host address too.

The group information is used when forwarding multicast data.
If there are no groups in the specific tunnel, Relay doesn't forward it.

Although Relay manages sources, it doesn't support the source filtering
feature. Because the reason to manage sources is just that in order
to manage group more correctly.

In the next patch, MLD part will be added.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: add data plane of amt interface

Before forwarding multicast traffic, the amt interface establishes between
gateway and relay. In order to establish, amt defined some message type
and those message flow looks like the below.

Gateway Relay
------- -----
: Request :
[1] | N |
|---------------------->|
| Membership Query | [2]
| N,MAC,gADDR,gPORT |
|<======================|
[3] | Membership Update |
| ({G:INCLUDE({S})}) |
|======================>|
| |
---------------------:-----------------------:---------------------
| | | |
| | *Multicast Data | *IP Packet(S,G) |
| | gADDR,gPORT |<-----------------() |
| *IP Packet(S,G) |<======================| |
| ()<-----------------| | |
| | | |
---------------------:-----------------------:---------------------
~ ~
~ Request ~
[4] | N' |
|---------------------->|
| Membership Query | [5]
| N',MAC',gADDR',gPORT' |
|<======================|
[6] | |
| Teardown |
| N,MAC,gADDR,gPORT |
|---------------------->|
| | [7]
| Membership Update |
| ({G:INCLUDE({S})}) |
|======================>|
| |
---------------------:-----------------------:---------------------
| | | |
| | *Multicast Data | *IP Packet(S,G) |
| | gADDR',gPORT' |<-----------------() |
| *IP Packet (S,G) |<======================| |
| ()<-----------------| | |
| | | |
---------------------:-----------------------:---------------------
| |
: :

1. Discovery
- Sent by Gateway to Relay
- To find Relay unique ip address
2. Advertisement
- Sent by Relay to Gateway
- Contains the unique IP address
3. Request
- Sent by Gateway to Relay
- Solicit to receive 'Query' message.
4. Query
- Sent by Relay to Gateway
- Contains General Query message.
5. Update
- Sent by Gateway to Relay
- Contains report message.
6. Multicast Data
- Sent by Relay to Gateway
- encapsulated multicast traffic.
7. Teardown
- Not supported at this time.

Except for the Teardown message, it supports all messages.

In the next patch, IGMP/MLD logic will be added.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

amt: add control plane of amt interface

It adds definitions and control plane code for AMT.
this is very similar to udp tunneling interfaces such as gtp, vxlan, etc.
In the next patch, data plane code will be added.

Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>