[LoRaWAN] Behaviour of Joins and LinkChecks

1. When they are powered, the transmitters send a JOIN *.
2. After 24 hours, they send a LinkCheckReq message which should be confirmed by a LinkCheckAck. And so on every 24 hours. As long as the LinkCheckReq are confirmed by a LinkCheckAck, the transmitter will not send a new JOIN.
3. If the LinkCheckReq message does not receive a LinkCheckAck response, then new LinkCheckReq will be sent in the process. If 6x LinkCheckReq receive no response, then the transmitter initiates a new JOIN procedure.

*JOIN: This is a network access phase LoRaWAN network that allows the network parameters to be dynamically renewed between the end device and the LoRa Server.