[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_ip.c b/net/ax25/ax25_ip.c
index 7f818bb..4d4ef35 100644
--- a/net/ax25/ax25_ip.c
+++ b/net/ax25/ax25_ip.c
@@ -171,7 +171,7 @@
 			src_c = *(ax25_address *)(bp + 8);
 
 			skb_pull(ourskb, AX25_HEADER_LEN - 1);	/* Keep PID */
-			ourskb->nh.raw = ourskb->data;
+			skb_reset_network_header(ourskb);
 
 			ax25=ax25_send_frame(
 			    ourskb,