[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/ax25/af_ax25.c b/net/ax25/af_ax25.c
index b1a4d60..14db01a 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1631,8 +1631,8 @@
 	if (!ax25_sk(sk)->pidincl)
 		skb_pull(skb, 1);		/* Remove PID */
 
-	skb->h.raw = skb->data;
-	copied     = skb->len;
+	skb_reset_transport_header(skb);
+	copied = skb->len;
 
 	if (copied > size) {
 		copied = size;