vlan: fix vlan_skb_recv()

Bruno Prémont found commit 9793241f
(vlan: Precise RX stats accounting) added a regression for non
hw accelerated vlans.

[   26.390576] BUG: unable to handle kernel NULL pointer dereference at (null)
[   26.396369] IP: [<df856b89>] vlan_skb_recv+0x89/0x280 [8021q]

vlan_dev_info() was used with original device, instead of
skb->dev. Also spotted by Américo Wang.
Reported-By: NBruno Prémont <bonbons@linux-vserver.org>
Tested-By: NBruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/8021q/vlan_dev.c

@@ -163,7 +163,7 @@ int vlan_skb_recv(struct sk_buff *skb, struct net_device *dev,
 		goto err_unlock;
 	}
 
-	rx_stats = per_cpu_ptr(vlan_dev_info(dev)->vlan_rx_stats,
+	rx_stats = per_cpu_ptr(vlan_dev_info(skb->dev)->vlan_rx_stats,
 			       smp_processor_id());
 	rx_stats->rx_packets++;
 	rx_stats->rx_bytes += skb->len;