[SK_BUFF]: Introduce skb_reset_network_header(skb)

For the common, open coded 'skb->nh.raw = skb->data' operation, so that we can
later turn skb->nh.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/net/ipv4/ipip.c b/net/ipv4/ipip.c
index 3ec5ce0..5f886c8 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -405,7 +405,7 @@
 	dst_release(skb2->dst);
 	skb2->dst = NULL;
 	skb_pull(skb2, skb->data - (u8*)eiph);
-	skb2->nh.raw = skb2->data;
+	skb_reset_network_header(skb2);
 
 	/* Try to guess incoming interface */
 	memset(&fl, 0, sizeof(fl));
@@ -487,7 +487,7 @@
 		secpath_reset(skb);
 
 		skb->mac.raw = skb->nh.raw;
-		skb->nh.raw = skb->data;
+		skb_reset_network_header(skb);
 		skb->protocol = htons(ETH_P_IP);
 		skb->pkt_type = PACKET_HOST;