Control whether QOS 0 should be queued when offline
In the definition of MQTT it is written, that QOS 0 messages are of type "fire and forget", so there is no acknowledgment of the receiver. However, these messages are sent to the server, ... or queued.
This means, that normally, when OTDT has currently no connection to the MQTT broker, messages of all types are queued for delivery (to the broker) when the broker gets back available.
So, if the connection between OTDT and the MQTT broker is a mobile connection, which is lost at a regular base, then the queue of messages becomes larger and larger where only a few messages are sent to the broker and the backlog becomes more and more. This is funny when sending QOS 0 messages, because they could be dropped (theoretically).
For this we added queue QOS 0 messages flag, which - when set to false - then drops QOS 0 message at OTDT without sending to the broker.