Changes to switchdev artifact can make a SPAN entry offloadable or
unoffloadable. To that end:

- Listen to SWITCHDEV_FDB_*_TO_BRIDGE notifications in addition to
  the *_TO_DEVICE ones, to catch whatever activity is sent to the
  bridge (likely by mlxsw itself).

  On each FDB notification, respin SPAN to reconcile it with the FDB
  changes.

- Also respin on switchdev port attribute changes (which currently
  covers changes to STP state of ports) and port object additions and
  removals.
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>