[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/message/fusion/mptlan.c b/drivers/message/fusion/mptlan.c
index b691292..d5b878d 100644
--- a/drivers/message/fusion/mptlan.c
+++ b/drivers/message/fusion/mptlan.c
@@ -753,7 +753,7 @@
 	/* Set the mac.raw pointer, since this apparently isn't getting
 	 * done before we get the skb. Pull the data pointer past the mac data.
 	 */
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 	skb_pull(skb, 12);
 
         dma = pci_map_single(mpt_dev->pcidev, skb->data, skb->len,
@@ -1549,7 +1549,7 @@
 	struct mpt_lan_ohdr *fch = (struct mpt_lan_ohdr *)skb->data;
 	struct fcllc *fcllc;
 
-	skb->mac.raw = skb->data;
+	skb_reset_mac_header(skb);
 	skb_pull(skb, sizeof(struct mpt_lan_ohdr));
 
 	if (fch->dtype == htons(0xffff)) {