[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>
diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c
index 418f169..3109376 100644
--- a/drivers/net/sky2.c
+++ b/drivers/net/sky2.c
@@ -1159,7 +1159,7 @@
 	count = sizeof(dma_addr_t) / sizeof(u32);
 	count += skb_shinfo(skb)->nr_frags * count;
 
-	if (skb_shinfo(skb)->gso_size)
+	if (skb_is_gso(skb))
 		++count;
 
 	if (skb->ip_summed == CHECKSUM_HW)