Three issues:
- when `hwaddress` is removed from an SVI (on top of a bridge), the svi
mac is not resetted back to the bridge mac: fixed
- when `hwaddress` is used on an svi, stale fdb enties were added with the
bridge mac: fixed
- on ifdown we were leaving a leftover fdb entry on the deleted svi: fixed
Signed-off-by: Julien Fortin <jfortin@nvidia.com>