bpf, sk_msg: Let ULP restore sk_proto and write_space callback

We don't need a fallback for when the socket is not using ULP.
tcp_update_ulp handles this case exactly the same as we do in
sk_psock_restore_proto. Get rid of the duplicated code.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200217121530.754315-2-jakub@cloudflare.com

include/linux/skmsg.h

@@ -361,16 +361,7 @@ static inline void sk_psock_restore_proto(struct sock *sk,
 	sk->sk_prot->unhash = psock->saved_unhash;
 
 	if (psock->sk_proto) {
-		struct inet_connection_sock *icsk = inet_csk(sk);
-		bool has_ulp = !!icsk->icsk_ulp_data;
-
-		if (has_ulp) {
-			tcp_update_ulp(sk, psock->sk_proto,
-				       psock->saved_write_space);
-		} else {
-			sk->sk_prot = psock->sk_proto;
-			sk->sk_write_space = psock->saved_write_space;
-		}
+		tcp_update_ulp(sk, psock->sk_proto, psock->saved_write_space);
 		psock->sk_proto = NULL;
 	} else {
 		sk->sk_write_space = psock->saved_write_space;