[SK_BUFF]: Introduce skb_transport_offset()

For the quite common 'skb->h.raw - skb->data' sequence.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index 2dd32a2..4427541 100644
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -160,7 +160,7 @@
 	rcu_read_lock();
 resubmit:
 	idev = ip6_dst_idev(skb->dst);
-	if (!pskb_pull(skb, skb->h.raw - skb->data))
+	if (!pskb_pull(skb, skb_transport_offset(skb)))
 		goto discard;
 	nhoff = IP6CB(skb)->nhoff;
 	nexthdr = skb_network_header(skb)[nhoff];