[SK_BUFF]: Introduce skb_reset_network_header(skb)

For the common, open coded 'skb->nh.raw = skb->data' operation, so that we can
later turn skb->nh.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 case, next 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/ax25_subr.c b/net/ax25/ax25_subr.c
index b6c577e..5fe9b2a 100644
--- a/net/ax25/ax25_subr.c
+++ b/net/ax25/ax25_subr.c
@@ -162,7 +162,7 @@
 
 	skb_reserve(skb, ax25->ax25_dev->dev->hard_header_len);
 
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 
 	/* Assume a response - address structure for DTE */
 	if (ax25->modulus == AX25_MODULUS) {
@@ -205,7 +205,7 @@
 		return;	/* Next SABM will get DM'd */
 
 	skb_reserve(skb, dev->hard_header_len);
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 
 	ax25_digi_invert(digi, &retdigi);