bpf: get rid of cgroup helper related ifdefs

As recently discussed during the task_under_cgroup_hierarchy() addition,
we should get rid of the ifdefs surrounding the bpf_skb_under_cgroup()
helper. If related functionality is not built-in, the helper cannot be
used anyway, which is also in line with what we do for all other helpers.

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

include/net/sock.h

@@ -1114,6 +1114,16 @@ static inline bool sk_stream_is_writeable(const struct sock *sk)
 	       sk_stream_memory_free(sk);
 }
 
+static inline int sk_under_cgroup_hierarchy(struct sock *sk,
+					    struct cgroup *ancestor)
+{
+#ifdef CONFIG_SOCK_CGROUP_DATA
+	return cgroup_is_descendant(sock_cgroup_ptr(&sk->sk_cgrp_data),
+				    ancestor);
+#else
+	return -ENOTSUPP;
+#endif
+}
 
 static inline bool sk_has_memory_pressure(const struct sock *sk)
 {