bpf: Sync bpf.h to tools/

Sync bpf_get_socket_cookie() related bpf UAPI changes to tools/.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>