Somehow when updating to this API, I missed the call to `successful`.
This doesn't seem to make a difference for most clients since
`create_immed` is normally used. But should correct anything using
`create`.
For the `drm` protocol, we can't construct an `ImportNotifier`, since
that is specifically based around `ZwpLinuxBufferParamsv1`. So we need a
new method for importing with that protocol.
This could be improved, but should match current behavior.
