skbuff: Fix offset error in skb_reorder_vlan_header

skb_reorder_vlan_header is called after the vlan header has
been pulled.  As a result the offset of the begining of
the mac header has been incrased by 4 bytes (VLAN_HLEN).
When moving the mac addresses, include this incrase in
the offset calcualation so that the mac addresses are
copied correctly.

Fixes: a6e18ff (vlan: Fix untag operations of stacked vlans with REORDER_HEADER off)
CC: Nicolas Dichtel <nicolas.dichtel@6wind.com>
CC: Patrick McHardy <kaber@trash.net>
Signed-off-by: Vladislav Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -4268,7 +4268,7 @@ static struct sk_buff *skb_reorder_vlan_header(struct sk_buff *skb)
 		return NULL;
 	}
 
-	memmove(skb->data - ETH_HLEN, skb->data - skb->mac_len,
+	memmove(skb->data - ETH_HLEN, skb->data - skb->mac_len - VLAN_HLEN,
 		2 * ETH_ALEN);
 	skb->mac_header += VLAN_HLEN;
 	return skb;