vlan: introduce *vlan_hwaccel_push_inside helpers

Use them to push skb->vlan_tci into the payload and avoid code
duplication.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 3611e60..ac48362 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2644,12 +2644,8 @@
 					  netdev_features_t features)
 {
 	if (vlan_tx_tag_present(skb) &&
-	    !vlan_hw_offload_capable(features, skb->vlan_proto)) {
-		skb = vlan_insert_tag_set_proto(skb, skb->vlan_proto,
-						vlan_tx_tag_get(skb));
-		if (skb)
-			skb->vlan_tci = 0;
-	}
+	    !vlan_hw_offload_capable(features, skb->vlan_proto))
+		skb = __vlan_hwaccel_push_inside(skb);
 	return skb;
 }