no voice when imsdroids join telepresence (MCU)

```
Two imsdroid(A and B) join telepresnece. One imsdroid A leaves the audio
conference, and joins the same conference again. The other imsdroid B can hear
any voice.

At first, voice can be heard from imsdroid B, but there is no voice heard after
imsdroid A leaves and joins the same conference. Between imsdroid A leaving and
joining the same conference, imsdroid B doesn't receive any audio rtp packets.

Is there anything wrong with low level module about audio in imsdroid?

Look forward to feedback.

Thanks!
```

Original issue reported on code.google.com by `andrewm...@gmail.com` on 31 Oct 2014 at 5:50

No files, tests, or entry points are named. Reproduce the two-imsdroid telepresence MCU scenario, then inspect the low-level audio and RTP handling around the leave-and-rejoin sequence; done means imsdroid B continues receiving audio RTP packets and can hear audio after imsdroid A rejoins.

Written by the indexing model from the issue text.