* Tweak adaptation to increase in propagation delay.
A couple of issues
- RTCP Sender Reports rate will vary based on underying track bitrate.
(at least in theory, not all entities will do it though, for example
SFU does standard rate of one per three seconds irrespective of track
bit rate). So, adapt the long term estimate of propagation delay delta
based on spacing of reports.
- Re-init of propagation delay to adapt to path change was taking the
last value before the switch. But, that one value could have been an
outlier and accepting it is not great. So, adapt spike time
propagation delay in a smoother fashion to ensure that all values
during spike contribute to the final value.
* clean up