vlan: reset headers on accel emulation path

It's after all necessary to do reset headers here. The reason is we
cannot depend that it gets reseted in __netif_receive_skb once skb is
reinjected. For incoming vlanids without vlan_dev, vlan_do_receive()
returns false with skb != NULL and __netif_reveive_skb continues, skb is
not reinjected.

This might be good material for 3.0-stable as well

Reported-by: Mike Auty <mike.auty@gmail.com>
Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan_core.c

@@ -167,6 +167,8 @@ struct sk_buff *vlan_untag(struct sk_buff *skb)
 	if (unlikely(!skb))
 		goto err_free;
 
+	skb_reset_network_header(skb);
+	skb_reset_transport_header(skb);
 	return skb;
 
 err_free: