selftest/tcp-ao: Add filter tests

selftest/tcp-ao: Add filter tests

Add tests that check if getsockopt(TCP_AO_GET_KEYS) returns the right
keys when using different filters.

Sample output:

> # ok 114 filter keys: by sndid, rcvid, address
> # ok 115 filter keys: by is_current
> # ok 116 filter keys: by is_rnext
> # ok 117 filter keys: by sndid, rcvid
> # ok 118 filter keys: correct nkeys when in.nkeys < matches

Acked-by: Dmitry Safonov <0x7f454c46@gmail.com>
Signed-off-by: Leo Stone <leocstone@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241021174652.6949-1-leocstone@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>