LoRa Server supports periodically requesting the device-status, using the
DevStatusReq mac-command specified by the LoRaWAN protocol.
A device will respond to this request by sending its battery status
(if available) and its demodulation signal-to-noise ratio in dB
for the last successfully received request.
When the device-status is available, it will be exposed to the application-server on each received uplink payload.
0- The end-device is connected to an external power source
1..254- The battery level, 1 being at minimum and 254 being at maximum
255- The end-device was not able to measure the battery level
The margin (Margin) is the demodulation signal-to-noise ratio in dB rounded to the nearest integer value for the last successfully received DevStatusReq command.