Turns a raw paging controls dict into Protobuf ClientPagingControls.

def _make_paging_message(controls):
        """Turns a raw paging controls dict into Protobuf ClientPagingControls.
        """

        return client_list_control_pb2.ClientPagingControls(
            start=controls.get('start', None),
            limit=controls.get('limit', None))