[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/ip_output.c b/net/ipv4/ip_output.c
index ddba857..32f1a23 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -593,7 +593,7 @@
 		ip_copy_metadata(skb2, skb);
 		skb_reserve(skb2, ll_rs);
 		skb_put(skb2, len + hlen);
-		skb2->nh.raw = skb2->data;
+		skb_reset_network_header(skb2);
 		skb2->h.raw = skb2->data + hlen;
 
 		/*
@@ -722,7 +722,7 @@
 		skb_put(skb,fragheaderlen + transhdrlen);
 
 		/* initialize network header pointer */
-		skb->nh.raw = skb->data;
+		skb_reset_network_header(skb);
 
 		/* initialize protocol header pointer */
 		skb->h.raw = skb->data + fragheaderlen;