8021q: fix mac_len recomputation in vlan_untag()

skb_reset_mac_len() relies on the value of the skb->network_header pointer,
therefore we must wait for such pointer to be recalculated before computing
the new mac_len value.
Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan_core.c

@@ -105,7 +105,6 @@ static struct sk_buff *vlan_reorder_header(struct sk_buff *skb)
 		return NULL;
 	memmove(skb->data - ETH_HLEN, skb->data - VLAN_ETH_HLEN, 2 * ETH_ALEN);
 	skb->mac_header += VLAN_HLEN;
-	skb_reset_mac_len(skb);
 	return skb;
 }
 
@@ -139,6 +138,8 @@ struct sk_buff *vlan_untag(struct sk_buff *skb)
 
 	skb_reset_network_header(skb);
 	skb_reset_transport_header(skb);
+	skb_reset_mac_len(skb);
+
 	return skb;
 
 err_free: