net: bridge: vlan: add rtnetlink group and notify support

Add a new rtnetlink group for bridge vlan notifications - RTNLGRP_BRVLAN
and add support for sending vlan notifications (both single and ranges).
No functional changes intended, the notification support will be used by
later patches.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>