[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/ipw2200.c b/drivers/net/wireless/ipw2200.c
index c878a2f..b04c56a 100644
--- a/drivers/net/wireless/ipw2200.c
+++ b/drivers/net/wireless/ipw2200.c
@@ -8133,7 +8133,7 @@
 		skb->dev = priv->ieee->dev;
 
 		/* Point raw at the ieee80211_stats */
-		skb->mac.raw = skb->data;
+		skb_reset_mac_header(skb);
 
 		skb->pkt_type = PACKET_OTHERHOST;
 		skb->protocol = __constant_htons(ETH_P_80211_STATS);