Add codec parameter to start_call() and convenience functions mt_call()
and calls() with FR as default. While at it, update the help text.
Instead of hardcoding FR in rtpsource, add an argument to set the codec
from mncc_mt_loadgen.py via CTRL call rtp_create. Hardcode FR in
mncc_mt_loadgen.py for now, a follow up patch will make it configurable
rtp_bridge=True triggers the automatic transmission of a MNCC_RTP_CREATE
when that call goes into ACTIVE state. We don't want this in the
case of mncc_mt_loadgen, as we perform this at a much sooner point in
This program (derived from mncc_test.py) is used to start MT calls
via the MNCC interface of OsmoMSC. Every calls RTP is connected
to the new 'rtpsource' process, which generates a realistic RTP
flow in terms of number of packets (20ms interval) and payload size.