aout: rework aout_RequestRestart arguments
The aout stream modules need to handle only 2 case:
- Restart only the aout stream modules (can be used to recover from error or other discontinuity from the system)
- Restart the aout stream module and the audio decoder (can be used to try new formats, likely one handled by pass-through)
This MR modify the aout_RequestRestart
arguments to handle only these 2 cases.