Add audio streaming support for generic PCM devices.

[charlyreen]

• Allow generic PCM devices to stream audio from ALSA via piKVM
• New config parameters in janus.plugin.ustreamer.jcfg:
  • pcm_path: Path in /dev/snd/ to PCM device
  • pcm_sampling_rate: Sampling rate
  • pcm_channels: Number of PCM channels

[mdevaev]

Has this code been tested? ~~Apparently, it shouldn't compile because of the wrong types.~~

And also, if I remember correctly, OPUS in RTP should always be stereo, shouldn't it?

[mdevaev]

Sup? Please take a look to my notes, and change type of pcm_sampling_rate to unsigned.