openvswitch: Fix pop_vlan action for double tagged frames

openvswitch: Fix pop_vlan action for double tagged frames

[ Upstream commit c48e74736fccf25fb32bb015426359e1c2016e3b ]

skb_vlan_pop() expects skb->protocol to be a valid TPID for double
tagged frames. So set skb->protocol to the TPID and let skb_vlan_pop()
shift the true ethertype into position for us.

Fixes: 5108bbaddc37 ("openvswitch: add processing of L3 packets")
Signed-off-by: Eric Garver <e@erig.me>
Reviewed-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>