net: use helpers to change sk_ack_backlog

Writers are holding a lock, but many readers do not.

Following patch will add appropriate barriers in
sk_acceptq_removed() and sk_acceptq_added().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/atm/signaling.c b/net/atm/signaling.c
index 6c11cdf..fbd0c5e 100644
--- a/net/atm/signaling.c
+++ b/net/atm/signaling.c
@@ -109,7 +109,7 @@ static int sigd_send(struct atm_vcc *vcc, struct sk_buff *skb)
 			dev_kfree_skb(skb);
 			goto as_indicate_complete;
 		}
-		sk->sk_ack_backlog++;
+		sk_acceptq_added(sk);
 		skb_queue_tail(&sk->sk_receive_queue, skb);
 		pr_debug("waking sk_sleep(sk) 0x%p\n", sk_sleep(sk));
 		sk->sk_state_change(sk);