selftests/net: enable lo.accept_local in psock_snd test

The psock_snd test sends and receives packets over loopback, and
the test results depend on parameter settings:
Set rp_filter=0,
or set rp_filter=1 and accept_local=1
so that the test will pass. Otherwise, this test will fail with
Resource temporarily unavailable:
sudo ./psock_snd.sh
dgram
tx: 128
rx: 142
./psock_snd: recv: Resource temporarily unavailable

For most distro kernel releases(like Ubuntu or Centos), the parameter
rp_filter is enabled by default, so it's necessary to enable the
parameter lo.accept_local in psock_snd test. And this test runs
inside a netns, changing a sysctl is fine.

Signed-off-by: luyun <luyun@kylinos.cn>
Reviewed-by: Jackie Liu <liuyun01@kylinos.cn>
Tested-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20220525031819.866684-1-luyun_611@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

selftests/net: add packet socket packet_snd test

Add regression tests for PF_PACKET transmission using packet_snd.

The TPACKET ring interface has tests for transmission and reception.
This is an initial stab at the same for the send call based interface.

Packets are sent over loopback, then read twice. The entire packet is
read from another packet socket and compared. The packet is also
verified to arrive at a UDP socket for protocol conformance.

The test sends a packet over loopback, testing the following options
(not the full cross-product):

- SOCK_DGRAM
- SOCK_RAW
- vlan tag
- qdisc bypass
- bind() and sendto()
- virtio_net_hdr
- csum offload (NOT actual csum feature, ignored on loopback)
- gso

Besides these basic functionality tests, the test runs from a set
of bounds checks, positive and negative. Running over loopback, which
has dev->min_header_len, it cannot generate variable length hhlen.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>