[NET]: Transform skb_queue_len() binary tests into skb_queue_empty()

This is part of the grand scheme to eliminate the qlen
member of skb_queue_head, and subsequently remove the
'list' member of sk_buff.

Most users of skb_queue_len() want to know if the queue is
empty or not, and that's trivially done with skb_queue_empty()
which doesn't use the skb_queue_head->qlen member and instead
uses the queue list emptyness as the test.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 29894c7..ddb6ce4 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1105,7 +1105,7 @@
 	struct sk_buff *skb;
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	NET_ADD_STATS_USER(LINUX_MIB_TCPPREQUEUED, skb_queue_len(&tp->ucopy.prequeue));
+	NET_INC_STATS_USER(LINUX_MIB_TCPPREQUEUED);
 
 	/* RX process wants to run with disabled BHs, though it is not
 	 * necessary */
@@ -1369,7 +1369,7 @@
 			 * is not empty. It is more elegant, but eats cycles,
 			 * unfortunately.
 			 */
-			if (skb_queue_len(&tp->ucopy.prequeue))
+			if (!skb_queue_empty(&tp->ucopy.prequeue))
 				goto do_prequeue;
 
 			/* __ Set realtime policy in scheduler __ */
@@ -1394,7 +1394,7 @@
 			}
 
 			if (tp->rcv_nxt == tp->copied_seq &&
-			    skb_queue_len(&tp->ucopy.prequeue)) {
+			    !skb_queue_empty(&tp->ucopy.prequeue)) {
 do_prequeue:
 				tcp_prequeue_process(sk);
 
@@ -1476,7 +1476,7 @@
 	} while (len > 0);
 
 	if (user_recv) {
-		if (skb_queue_len(&tp->ucopy.prequeue)) {
+		if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 			int chunk;
 
 			tp->ucopy.len = copied > 0 ? len : 0;