[NET]: Use prefetching in skb_queue_walk().

This patch changes skb_queue_walk() in the same manner
as in list_for_each() prefetch optimization, see
http://marc.theaimsgroup.com/?l=linux-kernel&m=110399132418587Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1077,9 +1077,9 @@ static inline void kunmap_skb_frag(void *vaddr)
 }
 
 #define skb_queue_walk(queue, skb) \
-		for (skb = (queue)->next, prefetch(skb->next);	\
-		     (skb != (struct sk_buff *)(queue));	\
-		     skb = skb->next, prefetch(skb->next))
+		for (skb = (queue)->next;					\
+		     prefetch(skb->next), (skb != (struct sk_buff *)(queue));	\
+		     skb = skb->next)
 
 
 extern struct sk_buff *skb_recv_datagram(struct sock *sk, unsigned flags,