WIP: Fix rtpjitterbuffer packet spacing calculations [ci skip]
Note that the unit tests haven't yet been updated accordingly and therefore will fail. I just wanted to get some preliminary feedback first, and hopefully have it tested in more real-life scenarios.
rtpjitterbuffer: Statistical packet spacing calculation
Instead of the previous heuristic calculation, calculate the average and standard deviation of a moving window of 50 samples, and then use μ + 1.5 * σ as a timeout.
rtpjitterbuffer: Fix expected arrival time of next seqnum
We should expect the next seqnum to arrive after a whole packet spacing. The previous calculation was using half the packet spacing, which doesn't go far enough.