mlxsw: spectrum: Add support for VLAN devices bridging

All the member VLAN devices in a bridge need to share the same vFID.

To achieve that, expand the vFID struct to include the associated bridge
device (or lack of) and allow one to lookup a vFID based on a bridge
device.

When joining a bridge, lookup the relevant vFID or create one if none
exists. Next, make the VLAN device use the vFID.

Leaving a bridge can either occur because a user removed the VLAN device
from a bridge or because the VLAN device was deleted by the user. In the
latter case the bridge's teardown sequence is invoked after the hardware
vPort is already gone. Therefore, when unlinking the VLAN device from
the real device, check if the associated vPort is bridged and act
accordingly. The bridge's notification will be ignored in this case.

Note that bridging a VLAN interface with an ordinary port netdev is
currently not supported, but not forbidden. This will be addressed in a
follow-up patchset.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>