selftests/net: convert ndisc_unsolicited_na_test.sh to run it in unique namespace

Here is the test result after conversion.

]# ./ndisc_unsolicited_na_test.sh
TEST: test_unsolicited_na: drop_unsolicited_na=0 accept_untracked_na=1 forwarding=1 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=0 accept_untracked_na=0 forwarding=0 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=0 accept_untracked_na=0 forwarding=1 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=0 accept_untracked_na=1 forwarding=0 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=1 accept_untracked_na=0 forwarding=0 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=1 accept_untracked_na=0 forwarding=1 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=1 accept_untracked_na=1 forwarding=0 [ OK ]
TEST: test_unsolicited_na: drop_unsolicited_na=1 accept_untracked_na=1 forwarding=1 [ OK ]

Tests passed: 8
Tests failed: 0

Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv6: Expand and rename accept_unsolicited_na to accept_untracked_na

RFC 9131 changes default behaviour of handling RX of NA messages when the
corresponding entry is absent in the neighbour cache. The current
implementation is limited to accept just unsolicited NAs. However, the
RFC is more generic where it also accepts solicited NAs. Both types
should result in adding a STALE entry for this case.

Expand accept_untracked_na behaviour to also accept solicited NAs to
be compliant with the RFC and rename the sysctl knob to
accept_untracked_na.

Fixes: f9a2fb73318e ("net/ipv6: Introduce accept_unsolicited_na knob to implement router-side changes for RFC9131")
Signed-off-by: Arun Ajith S <aajith@arista.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20220530101414.65439-1-aajith@arista.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv6: Introduce accept_unsolicited_na knob to implement router-side changes for RFC9131

Add a new neighbour cache entry in STALE state for routers on receiving
an unsolicited (gratuitous) neighbour advertisement with
target link-layer-address option specified.
This is similar to the arp_accept configuration for IPv4.
A new sysctl endpoint is created to turn on this behaviour:
/proc/sys/net/ipv6/conf/interface/accept_unsolicited_na.

Signed-off-by: Arun Ajith S <aajith@arista.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>