[NET] gso: Add skb_is_gso

This patch adds the wrapper function skb_is_gso which can be used instead
of directly testing skb_shinfo(skb)->gso_size.  This makes things a little
nicer and allows us to change the primary key for indicating whether an skb
is GSO (if we ever want to do that).

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1001,7 +1001,7 @@ static inline int net_gso_ok(int features, int gso_type)
 
 static inline int skb_gso_ok(struct sk_buff *skb, int features)
 {
-	return net_gso_ok(features, skb_shinfo(skb)->gso_size ?
+	return net_gso_ok(features, skb_is_gso(skb) ?
 				    skb_shinfo(skb)->gso_type : 0);
 }
 

include/linux/skbuff.h

@@ -1455,5 +1455,10 @@ static inline void skb_init_secmark(struct sk_buff *skb)
 { }
 #endif
 
+static inline int skb_is_gso(const struct sk_buff *skb)
+{
+	return skb_shinfo(skb)->gso_size;
+}
+
 #endif	/* __KERNEL__ */
 #endif	/* _LINUX_SKBUFF_H */