timecodestamper: Refactor LTC audio waiting and properly handle live inputs

timecodestamper: Refactor LTC audio waiting and properly handle live inputs

If one of the inputs is live, add a latency of 2 frames to the video
stream and wait on the clock for that much time to pass to allow for the
LTC audio to be ahead.

In case of live LTC, don't do any waiting but only ensure that we don't
overflow the LTC queue.

Also in non-live LTC audio mode, flush too old items from the LTC queue
if the video is actually ahead instead of potentially waiting forever.
This could've happened if there was a bigger gap in the video stream.