[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/tcp_input.c b/net/ipv4/tcp_input.c
index 0019083..5da823a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3634,7 +3634,8 @@
 			return;
 
 		skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
-		nskb->nh.raw = nskb->data + (skb_network_header(skb) - skb->head);
+		skb_set_network_header(nskb,
+				       skb_network_header(skb) - skb->head);
 		nskb->h.raw = nskb->data + (skb->h.raw - skb->head);
 
 		skb_reserve(nskb, header);