selftests/bpf: lsm_cgroup functional test

Functional test that exercises the following:

1. apply default sk_priority policy
2. permit TX-only AF_PACKET socket
3. cgroup attach/detach/replace
4. reusing trampoline shim

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/r/20220628174314.1216643-12-sdf@google.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>