p2p: Fix public IP hack for browser environments

[albrow]

https://ifconfig.me responds with different results depending on the value of the User-Agent header. For browser environments, it responds with HTML and for non-browser environments it responds with your IP address in plain text. Adding /ip to the URL results in the same behavior regardless of user agent.

[fabioberger]

@albrow does this return a sensible, usable response? If not, why not just skip this step if in the browser?

[albrow]

does this return a sensible, usable response? If not, why not just skip this step if in the browser?

Good point; probably not. It might be useful for WebRTC connections but I think the ICE process is already designed to do this.

Nonetheless we should still use the url with the /ip suffix. It's more reliable and doesn't depend on your User-Agent (which could still change slightly for different platforms even for non-browser peers).