ao/wasapi: add ao hotplug

[kevmitch]

Create a second copy of the change_notify structure for the hotplug
ao. The hotplug change_notify is distinguished by not having its
"monitored" member set since it does not watch a single device.

[ghost]

Does this consider the fact that calling ao_request_reload() on the hotplug ao does nothing? (I'm not sure if you rely on this somehow, but it seems it can be called.)

[kevmitch]

I have ensured that calling ao_request_reload() on hotplug and ao_hotplug_event on the real ao doesn't happen. In the hotplug "monitored" is null. I've made it a little clearer by putting the request_reload into else if clauses where appropriate.

Should I just add an is_hotplug member to make this clearer?

[ghost]

Should I just add an is_hotplug member to make this clearer?

Yep, sounds like a good idea.

Btw., the usual prefix here is ao_wasapi (with a _, not /).

Other than that I have no further comments.