bridge: Add filtering support for default_pvid

Currently when vlan filtering is turned on on the bridge, the bridge
will drop all traffic untill the user configures the filter.  This
isn't very nice for ports that don't care about vlans and just
want untagged traffic.

A concept of a default_pvid was recently introduced.  This patch
adds filtering support for default_pvid.   Now, ports that don't
care about vlans and don't define there own filter will belong
to the VLAN of the default_pvid and continue to receive untagged
traffic.

This filtering can be disabled by setting default_pvid to 0.

Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>