net: add scheduler sync hint to tcp_prequeue().

Decreases the odds wakee will suffer from frequent cache misses.
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/tcp.h

@@ -939,7 +939,7 @@ static inline int tcp_prequeue(struct sock *sk, struct sk_buff *skb)
 
 		tp->ucopy.memory = 0;
 	} else if (skb_queue_len(&tp->ucopy.prequeue) == 1) {
-		wake_up_interruptible_poll(sk->sk_sleep,
+		wake_up_interruptible_sync_poll(sk->sk_sleep,
 					   POLLIN | POLLRDNORM | POLLRDBAND);
 		if (!inet_csk_ack_scheduled(sk))
 			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,