net: dsa: fix SWITCHDEV_ATTR_ID_BRIDGE_VLAN_FILTERING getting ignored

The bridge emits VLAN filtering events and quite a few others via
switchdev with orig_dev = br->dev. After the blamed commit, these events
started getting ignored.

The point of the patch was to not offload switchdev objects for ports
that didn't go through dsa_port_bridge_join, because the configuration
is unsupported:
- ports that offload a bonding/team interface go through
  dsa_port_bridge_join when that bonding/team interface is later bridged
  with another switch port or LAG
- ports that don't offload LAG don't get notified of the bridge that is
  on top of that LAG.

Sadly, a check is missing, which is that the orig_dev is equal to the
bridge device. This check is compatible with the original intention,
because ports that don't offload bridging because they use a software
LAG don't have dp->bridge_dev set.

On a semi-related note, we should not offload switchdev objects or
populate dp->bridge_dev if the driver doesn't implement .port_bridge_join
either. However there is no regression associated with that, so it can
be done separately.

Fixes: 5696c8ae

 ("net: dsa: Don't offload port attributes on standalone ports")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Tobias Waldekranz <tobias@waldekranz.com>
Tested-by: Tobias Waldekranz <tobias@waldekranz.com>
Link: https://lore.kernel.org/r/20210202233109.1591466-1-olteanv@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>