libbpf: Add support for BPF_CGROUP_INET_SOCK_RELEASE

Add auto-detection for the cgroup/sock_release programs.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200706230128.4073544-3-sdf@google.com