Disconnect mqtt

Disconnect Mqtt, the premise is that this mqtt connection must have been established at last time by correct Iot_id, Iot_pwd.

Request:

"|4|1|4|\r"

Returns:

"|4|1|4|1|\r" Successfully disconnected

"|4|1|4|2|\r" Fail to disconnect

Arduino Sample:

softSerial.print("|4|1|4|\r");