The timer code used to trigger periodic statistics message sending used
ITTI. Together with a high frequency reporting (e.g. 1ms), this resulted
in high CPU usage. This commit reimplements this:
* using a thread that is synchronized to the RU (if there is no MAC, we
assume there is no RU generating a tick so we create the tick source
ourselves)
* no RB trees but plain arrays
* smaller interface for users
* slight user interface changes
* remove stopped timer state: such timer might be simply removed
* remove one-shot timers
* only set up timer for sending requests
* simplify interface for timer setup
* on timer expiry, do not pass through stats request function but
directly send the reply
* Remove whatever report structure and use stats request directly for
inferring the data to send
Robert Schmidt