Turn off relay.

async def turn_off(self, switch=None):
        """Turn off relay."""
        if switch is not None:
            switch = codecs.decode(switch.rjust(2, '0'), 'hex')
            packet = self.protocol.format_packet(b"\x10" + switch + b"\x02")
        else:
            packet = self.protocol.format_packet(b"\x0b")
        states = await self._send(packet)
        return states