openvswitch: Consistently include VLAN header in flow and port stats.

Until now, when VLAN acceleration was in use, the bytes of the VLAN header
were not included in port or flow byte counters.  They were however
included when VLAN acceleration was not used.  This commit corrects the
inconsistency, by always including the VLAN header in byte counters.

Previous discussion at
http://openvswitch.org/pipermail/dev/2014-December/049521.html

Reported-by: Motonori Shindo <mshindo@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Reviewed-by: Flavio Leitner <fbl@sysclose.org>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>