Audio stutter when using audio switchboard with narrowband codec (thanks Bogdan Krakowski for the report)

[bennylp]

Audio stutter is observed when configuring pjsua to use audio switchboard instead of the default conference bridge, and when narrowband clock rate is used by the media (for example, play file).

To reproduce:

1. enable switchboard, by declaring this in config_site.h:

   #define PJMEDIA_CONF_USE_SWITCH_BOARD	1
   

2. run pjsua, enable only PCMA:

   $ pjsua --dis-codec * --add-codec pcmu
   

3. call a destination, and hear the audio.

This was tested on Linux Ubuntu 09.10 64bit.