[SK_BUFF]: Introduce skb_network_header()

For the places where we need a pointer to the network header, it is still legal
to touch skb->nh.raw directly if just adding to, subtracting from or setting it
to another layer header.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index 02647fe..8a6b0e7 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -326,7 +326,7 @@
 		case TCF_LAYER_LINK:
 			return skb->data;
 		case TCF_LAYER_NETWORK:
-			return skb->nh.raw;
+			return skb_network_header(skb);
 		case TCF_LAYER_TRANSPORT:
 			return skb->h.raw;
 	}