bridge: Add SWITCHDEV_FDB_FLUSH_TO_BRIDGE notifier

so the switchdev can notifiy the bridge to flush non-permanent fdb entries
for this port. This is useful whenever the hardware fdb of the switchdev
is reset, but the netdev and the bridgeport are not deleted.

Note that this has the same effect as the IFLA_BRPORT_FLUSH attribute.

CC: Jiri Pirko <jiri@resnulli.us>
CC: Ivan Vecera <ivecera@redhat.com>
CC: Roopa Prabhu <roopa@nvidia.com>
CC: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Acked-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>