"WebRTC WG has asked for privacy and security considerations around the disclosure of a user's local IP address in #webrtc "

https://www.w3.org/wiki/Privacy/IPAddresses

You can prevent this with, for example, #ublockorigin or #privacybadger - see https://github.com/gorhill/uBlock/wiki/Prevent-WebRTC-from-leaking-local-IP-address for some discussion.