[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/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
index 4ab7b40..74062dc 100644
--- a/drivers/block/aoe/aoecmd.c
+++ b/drivers/block/aoe/aoecmd.c
@@ -27,7 +27,8 @@
 
 	skb = alloc_skb(len, GFP_ATOMIC);
 	if (skb) {
-		skb->nh.raw = skb->mac.raw = skb->data;
+		skb_reset_mac_header(skb);
+		skb->nh.raw = skb->data;
 		skb->protocol = __constant_htons(ETH_P_AOE);
 		skb->priority = 0;
 		skb->next = skb->prev = NULL;