[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/e1000/e1000_main.c b/drivers/net/e1000/e1000_main.c
index f77624f..1f34d06 100644
--- a/drivers/net/e1000/e1000_main.c
+++ b/drivers/net/e1000/e1000_main.c
@@ -2394,7 +2394,7 @@
 	uint8_t ipcss, ipcso, tucss, tucso, hdr_len;
 	int err;
 
-	if (skb_shinfo(skb)->gso_size) {
+	if (skb_is_gso(skb)) {
 		if (skb_header_cloned(skb)) {
 			err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC);
 			if (err)
@@ -2519,7 +2519,7 @@
 		 * tso gets written back prematurely before the data is fully
 		 * DMA'd to the controller */
 		if (!skb->data_len && tx_ring->last_tx_tso &&
-		    !skb_shinfo(skb)->gso_size) {
+		    !skb_is_gso(skb)) {
 			tx_ring->last_tx_tso = 0;
 			size -= 4;
 		}
@@ -2806,8 +2806,7 @@
 
 #ifdef NETIF_F_TSO
 	/* Controller Erratum workaround */
-	if (!skb->data_len && tx_ring->last_tx_tso &&
-	    !skb_shinfo(skb)->gso_size)
+	if (!skb->data_len && tx_ring->last_tx_tso && !skb_is_gso(skb))
 		count++;
 #endif