UI: Correctly toggle audio multi-track buttons

This toggles audio multi track display in Output settings when:
1. When there is a signal that a stream service is changed to a non
custom one. Indeed multi-track audio is only available with Custom
service and only with SRT or RIST protocols.
2. When a Custom service is picked, and SRT or RIST are detected in the
server URL.
3. When Stream settings are saved when one hits Apply.
This is in addition to the toggling done when loading Stream Settings.

Signed-off-by: pkv <pkv@obsproject.com>