alsa_sound :Starting "UsbRecordingThread" if not started

- Recorder stop() was getting called in hangout app before the
  call got connected, this will stop UsbRecordingThread.
  Recorder set() is called with a sample rate of 48k due to which
  the USB recording thread doesnt get re-started because for VOIP
  the sample rate expected is 8/16k.

- UsbRecordingThread has to get started when the call
  gets connected.

Change-Id: I12c4d1f473224de7df2041f22fdc45cf77ac4acb
CRs-Fixed: 516270