mlxsw: spectrum_switchdev: Change switchdev notifier API

The current API for sending switchdev notifications implies only FDB
add/del. In order to support notification about successful FDB offload
the API is changed.

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