* 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
* give the correct UE_id instead an index of the protobuf message (they can
diverge from each other)
* in the PDCP part of the RAN API, the RAN API has to make the conversion UE_id
(MAC) to UID (PDCP)
* a follow up commit could clean up the interfaces:
- the MAC functions take the UE_id
- the RRC functions take the RNTI
- the PDCP functions take the UID
this would mean the caller has to find those ID but would decrease
computations since the RAN API functions do not have to do that themselves