* add mac layer counter
* add more counters and Doxygen for MAC counters
* have a seperate counter for acked data transmission and refine the code based on the comments
* refine counters for acked and unacked transmissions
* fix check test error
* refine code style and use VerifyOrExit to exit
* move all events tracker to tx/rx done task, and add more counters
* fix other error counter
* refine counters structure to be clearer
* add Doxygen for the added thread errors
* fix conflicts
* Add an LQI field to the radio packet structure.
* Add an LQI field to the ThreadMessageInfo.
* Add an LQI field to the scan result.
* Print LQI value in CLI scan result.