Merge branch 'socket-lookup-cg_sock'

Andrey Ignatov says:

====================
This patch set makes bpf_sk_lookup_tcp, bpf_sk_lookup_udp and
bpf_sk_release helpers available in programs of type
BPF_PROG_TYPE_CGROUP_SOCK_ADDR.

Patch 1 is a fix for bpf_sk_lookup_udp that was already merged to bpf
(stable) tree. Here it's prerequisite for patch 3.

Patch 2 is the main patch in the set, it makes the helpers available for
BPF_PROG_TYPE_CGROUP_SOCK_ADDR and provides more details about use-case.

Patch 3 adds selftest for new functionality.

v1->v2:
- remove "Split bpf_sk_lookup" patch since it was already split by:
  commit c8123ead13a5 ("bpf: Extend the sk_lookup() helper to XDP
  hookpoint.");
- avoid unnecessary bpf_sock_addr_sk_lookup function.
====================

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