vlan: Update skb->mac_header in __vlan_put_tag().

After moving mac addresses in __vlan_put_tag() skb->mac_header needs
to be updated.

Reported-by: Karl Hiramoto <karl@hiramoto.org>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index f8ff918..e1ff5b1 100644
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -210,6 +210,7 @@
 
 	/* Move the mac addresses to the beginning of the new header. */
 	memmove(skb->data, skb->data + VLAN_HLEN, 2 * VLAN_ETH_ALEN);
+	skb->mac_header -= VLAN_HLEN;
 
 	/* first, the ethernet type */
 	veth->h_vlan_proto = htons(ETH_P_8021Q);