[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/chelsio/sge.c b/drivers/net/chelsio/sge.c
index 87f94d9..61b3754 100644
--- a/drivers/net/chelsio/sge.c
+++ b/drivers/net/chelsio/sge.c
@@ -1417,7 +1417,7 @@
 	struct cpl_tx_pkt *cpl;
 
 #ifdef NETIF_F_TSO
-	if (skb_shinfo(skb)->gso_size) {
+	if (skb_is_gso(skb)) {
 		int eth_type;
 		struct cpl_tx_pkt_lso *hdr;