Start transmitting message (add to list if needed).

def start(self):
        """Start transmitting message (add to list if needed)."""
        if self._index is None:
            self._index = ctypes.c_uint32()
            _canlib.canSchedulerAddMessage(self._scheduler,
                                           self._msg,
                                           self._index)
        _canlib.canSchedulerStartMessage(self._scheduler,
                                         self._index,
                                         self._count)