Updates libjitsi to a version which uses a 2-channel format
for the opus/rtp format. This breaks opus compatibility with older versions,
because older versions use a 1-channel format.

The change is necessary, because
the payload-rtp-opus draft mandates that 2 channels be advertised.
Implements a workaround which fixes the number of channels
on Colibri payload-type elements with name="opus".