[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/ipv6/xfrm6_mode_tunnel.c b/net/ipv6/xfrm6_mode_tunnel.c
index 5bb0677..8ce5ef2 100644
--- a/net/ipv6/xfrm6_mode_tunnel.c
+++ b/net/ipv6/xfrm6_mode_tunnel.c
@@ -53,7 +53,7 @@
 	skb_push(skb, x->props.header_len);
 	iph = skb->nh.ipv6h;
 
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 	top_iph = skb->nh.ipv6h;
 	skb->nh.raw = &top_iph->nexthdr;
 	skb->h.ipv6h = top_iph + 1;
@@ -111,7 +111,7 @@
 	old_mac = skb_mac_header(skb);
 	skb_set_mac_header(skb, -skb->mac_len);
 	memmove(skb_mac_header(skb), old_mac, skb->mac_len);
-	skb->nh.raw = skb->data;
+	skb_reset_network_header(skb);
 	err = 0;
 
 out: