[SK_BUFF]: Introduce skb_reset_mac_header(skb)

For the common, open coded 'skb->mac.raw = skb->data' operation, so that we can
later turn skb->mac.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/drivers/net/wireless/strip.c b/drivers/net/wireless/strip.c
index f5ce1c6..2a299a0 100644
--- a/drivers/net/wireless/strip.c
+++ b/drivers/net/wireless/strip.c
@@ -2009,7 +2009,7 @@
 		       packetlen);
 		skb->dev = get_strip_dev(strip_info);
 		skb->protocol = header->protocol;
-		skb->mac.raw = skb->data;
+		skb_reset_mac_header(skb);
 
 		/* Having put a fake header on the front of the sk_buff for the */
 		/* benefit of tools like tcpdump, skb_pull now 'consumes' that  */