[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/s390/net/ctcmain.c b/drivers/s390/net/ctcmain.c
index 0d6d5fc..787c013 100644
--- a/drivers/s390/net/ctcmain.c
+++ b/drivers/s390/net/ctcmain.c
@@ -455,7 +455,7 @@
 			return;
 		}
 		skb_put(pskb, header->length);
-		pskb->mac.raw = pskb->data;
+		skb_reset_mac_header(pskb);
 		len -= header->length;
 		skb = dev_alloc_skb(pskb->len);
 		if (!skb) {
@@ -473,7 +473,7 @@
 			return;
 		}
 		memcpy(skb_put(skb, pskb->len), pskb->data, pskb->len);
-		skb->mac.raw = skb->data;
+		skb_reset_mac_header(skb);
 		skb->dev = pskb->dev;
 		skb->protocol = pskb->protocol;
 		pskb->ip_summed = CHECKSUM_UNNECESSARY;