Add uid and cookie bpf helper to cg_skb_func_proto

BPF helper functions get_socket_cookie and get_socket_uid can be
used for network traffic classifications, among others. Expose
them also to programs of type BPF_PROG_TYPE_CGROUP_SKB. As of
commit 8f917bba0042 ("bpf: pass sk to helper functions") the
required skb->sk function is available at both cgroup bpf ingress
and egress hooks. With these two new helper, cg_skb_func_proto is
effectively the same as sk_filter_func_proto.

Change since V1:
Instead of add the helper to cg_skb_func_proto, redirect the
cg_skb_func_proto to sk_filter_func_proto since all helper function
in sk_filter_func_proto are applicable to cg_skb_func_proto now.

Signed-off-by: Chenbo Feng <fengc@google.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -2766,12 +2766,7 @@ xdp_func_proto(enum bpf_func_id func_id)
 static const struct bpf_func_proto *
 cg_skb_func_proto(enum bpf_func_id func_id)
 {
-	switch (func_id) {
-	case BPF_FUNC_skb_load_bytes:
-		return &bpf_skb_load_bytes_proto;
-	default:
-		return bpf_base_func_proto(func_id);
-	}
+	return sk_filter_func_proto(func_id);
 }
 
 static const struct bpf_func_proto *