bridge: Prepare for 802.1ad vlan filtering support

This enables a bridge to have vlan protocol informantion and allows vlan
tag manipulation (retrieve, insert and remove tags) according to the vlan
protocol.

Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>