[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/include/net/udp.h b/include/net/udp.h
index 4a9699f..4906ed7 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -89,8 +89,8 @@
  */
 static inline __wsum udp_csum_outgoing(struct sock *sk, struct sk_buff *skb)
 {
-	__wsum csum = csum_partial(skb->h.raw, sizeof(struct udphdr), 0);
-
+	__wsum csum = csum_partial(skb_transport_header(skb),
+				   sizeof(struct udphdr), 0);
 	skb_queue_walk(&sk->sk_write_queue, skb) {
 		csum = csum_add(csum, skb->csum);
 	}