The current version of the CC26xx web demo publishes over MQTT the default parent's IPv6 address and the last observed RSSI of this link. This is collected by active probing (periodic ping).
This commit brings the probing functionality to the example's main code module. The MQTT client keeps publishing as previously, but we now also export the same information through CoAP resources. Configuration is still possible through the example's web server.
* Query the sensor about its state, rather than using variables in the driver
* Correctly put the sensor to deep sleep
* Fix doxygen comments
* Don't turn off the sensor in examples since it is no longer needed
