net: skb_trim explicitely check the linearity instead of data_len

The purpose of the check on data_len is to check linearity, so use the inline
helper for this. No overhead and more explicit.
Signed-off-by: NEmmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1442,7 +1442,7 @@ extern int ___pskb_trim(struct sk_buff *skb, unsigned int len);
 
 static inline void __skb_trim(struct sk_buff *skb, unsigned int len)
 {
-	if (unlikely(skb->data_len)) {
+	if (unlikely(skb_is_nonlinear(skb))) {
 		WARN_ON(1);
 		return;
 	}