[NET]: Optimize pskb_trim_rcsum()

Since packets almost never contain extra garbage at the end, it is
worthwhile to optimize for that case.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1167,7 +1167,7 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
 
 static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
 {
-	if (len >= skb->len)
+	if (likely(len >= skb->len))
 		return 0;
 	if (skb->ip_summed == CHECKSUM_HW)
 		skb->ip_summed = CHECKSUM_NONE;