Add an option to selectively allow UDP in either sending or receiving

Context

#4881

I'm operating a worldwide server and there are unique connectivity issue in different regions. I want to ensure that users have best voice quality while under connection budget, and that involves different settings for different regions.

Description

I need to have individual switches that controls the inbound and outbound UDP connections.

Mumble component

Client

OS-specific?

No

Additional information

There might be ways to automatically detect this but I have seen the connection detail of a few users having issue and the UDP packet statistics does not show large drops. Having individual switches helps make the situation more manageable.

Or it's better if we can let server decide this via the IP address of the user or other measures.