audiod: Stop stream immediately when being switched off.

audiod: Stop stream immediately when being switched off.

When para_audiod enters off/standby mode, we stop the receiver
but continue to filter and write data already received until the
input queue has drained. This can take several seconds, which may
be annoying.

To stop the stream immediately, stop the writer(s) rather than the
receiver. We still only stop the receiver when the server has paused
or stopped the stream because we don't want to discard any data in
this case.