[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/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2c5b445..3bc74ce 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -147,7 +147,7 @@
 
 int ip6_output(struct sk_buff *skb)
 {
-	if ((skb->len > dst_mtu(skb->dst) && !skb_shinfo(skb)->gso_size) ||
+	if ((skb->len > dst_mtu(skb->dst) && !skb_is_gso(skb)) ||
 				dst_allfrag(skb->dst))
 		return ip6_fragment(skb, ip6_output2);
 	else
@@ -229,7 +229,7 @@
 	skb->priority = sk->sk_priority;
 
 	mtu = dst_mtu(dst);
-	if ((skb->len <= mtu) || ipfragok || skb_shinfo(skb)->gso_size) {
+	if ((skb->len <= mtu) || ipfragok || skb_is_gso(skb)) {
 		IP6_INC_STATS(IPSTATS_MIB_OUTREQUESTS);
 		return NF_HOOK(PF_INET6, NF_IP6_LOCAL_OUT, skb, NULL, dst->dev,
 				dst_output);