[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/appletalk/aarp.c b/net/appletalk/aarp.c
index d89d62f..d4e5ba2 100644
--- a/net/appletalk/aarp.c
+++ b/net/appletalk/aarp.c
@@ -539,7 +539,7 @@
 	int hash;
 	struct aarp_entry *a;
 
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 
 	/* Check for LocalTalk first */
 	if (dev->type == ARPHRD_LOCALTLK) {