When the possibility for it to be true will exist, _all_ switchdev
drivers will need to be updated to ignore that (mlxsw, cpss, ocelot,
rocker, prestera, etc etc), not just DSA. And you don't need to
propagate the is_locked flag to all individual DSA sub-drivers when none
care about is_locked in the ADD_TO_DEVICE direction, you can just ignore
within DSA until needed otherwise.