[SK_BUFF]: Introduce skb_transport_header(skb)

For the places where we need a pointer to the transport header, it is
still legal to touch skb->h.raw directly if just adding to,
subtracting from or setting it to another layer header.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 39216e6..e6a9e45 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -619,7 +619,7 @@
 		skb_reset_mac_header(skb);
 		__pskb_pull(skb, offset);
 		skb_reset_network_header(skb);
-		skb_postpull_rcsum(skb, skb->h.raw, offset);
+		skb_postpull_rcsum(skb, skb_transport_header(skb), offset);
 		skb->pkt_type = PACKET_HOST;
 #ifdef CONFIG_NET_IPGRE_BROADCAST
 		if (MULTICAST(iph->daddr)) {