Convert to an from pulse enum to id in the message layer so that we
can always just deal with native spa types.
Use the channelmap in stream-restore
Parse the channelmap from properties.
Parse the format_info in CREATE_STREAM and use this to negotiate
the stream. Implement channel_map parsing.
Delay setting up the buffer attributes until we have negotiated a
format.
Makes GStreamer pulsesink work (rhythmbox,... )