net: don not detour through struct sock to find the poll waitqueue

For any open socket file descriptor sock->sk->sk_wq->wait will always
point to sock->wq->wait.  That means we can do the shorter dereference
and removal a NULL check and don't have to not worry about any RCU
protection.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2064,10 +2064,9 @@ static inline bool skwq_has_sleeper(struct socket_wq *wq)
 static inline void sock_poll_wait(struct file *filp, poll_table *p)
 {
 	struct socket *sock = filp->private_data;
-	wait_queue_head_t *wq = sk_sleep(sock->sk);
 
-	if (!poll_does_not_wait(p) && wq) {
-		poll_wait(filp, wq, p);
+	if (!poll_does_not_wait(p)) {
+		poll_wait(filp, &sock->wq->wait, p);
 		/* We need to be sure we are in sync with the
 		 * socket flags modification.
 		 *