net: devlink: add not cleared type warning to port unregister

By the time port unregister is called. There should be no type set. Make
sure that the driver cleared it before and warn in case it didn't. This
enforces symmetricity with type set and port register.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>