webrtcbin: request to expose setting the min and max port range for host candidates in libnice

I wanted to request the ability to specify the local port range used for ICE host candidate selection used by webrtcbin.

This feature is available in libnice via the nice_agent_set_port_range() function.

Ideally, it could be expose to the webrtcbin plugin as optional properties:

webrtcbin min-rtp-port=10000 max-rtp-port=10000 min-rtcp-port=10001 max-rtcp-port=10001 name=sendrecv...

The use case for this would be to allow use webrtcbin in client-server applications without a STUN/TURN servers, where a fixed port or port range can be known and available, and where NAT hole punching is not working reliably, or where a public port can be set in a different way.

Specifically, my use case is using gstreamer with webrtcbin within Docker containers where a public port can be assigned to a fixed container port. Setting the min-port and max-port allows for having a fixed port inside the container. (NAT hole punching with Docker networks has not worked reliably).

I can help contribute a patch to this if there is interest in adding this. Thank you!