[webrtc-stats] Request to add neteq waiting time to stats report (#427)

wssjwl has just created a new issue for https://github.com/w3c/webrtc-stats:

== Request to add neteq waiting time to stats report ==
Stats to be added

max_waiting_time_ms
mean_waiting_time_ms

Justification
* These are useful to understand how network was operating.  Existing metrics such as plc/cng/plccng/etc do not provide enough insight that waiting time provides.
* The metrics have already been calculated and have been collected by acm_receiver.  However, it was dropped by audio_receive_stream.  Hence, it is not being used for any purpose.  There are only a few steps away from making it available in the stats report.

Please view or discuss this issue at https://github.com/w3c/webrtc-stats/issues/427 using your GitHub account