[SK_BUFF]: Introduce skb_set_network_header

For the cases where the network header is being set to a offset from skb->data.

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 eae2284..15de9d4 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -928,9 +928,9 @@
 			 *	Find where to start putting bytes.
 			 */
 			data = skb_put(skb, fraglen);
-			skb->nh.raw = data + exthdrlen;
+			skb_set_network_header(skb, exthdrlen);
+			skb->h.raw = skb->nh.raw + fragheaderlen;
 			data += fragheaderlen;
-			skb->h.raw = data + exthdrlen;
 
 			if (fraggap) {
 				skb->csum = skb_copy_and_csum_bits(