[SK_BUFF]: Introduce skb_reset_transport_header(skb)

For the common, open coded 'skb->h.raw = skb->data' operation, so that we can
later turn skb->h.raw into a offset, reducing the size of struct sk_buff in
64bit land while possibly keeping it as a pointer on 32bit.

This one touches just the most simple cases:

skb->h.raw = skb->data;
skb->h.raw = {skb_push|[__]skb_pull}()

The next ones will handle the slightly more "complex" cases.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index b4cad50..13739cd 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1002,7 +1002,8 @@
 	 * transport header to point to ESP.  Keep UDP on the stack
 	 * for later.
 	 */
-	skb->h.raw = __skb_pull(skb, len);
+	__skb_pull(skb, len);
+	skb_reset_transport_header(skb);
 
 	/* modify the protocol (it's ESP!) */
 	iph->protocol = IPPROTO_ESP;