Ask for user media on mobile for VPN support

[Legend-Master]

If no getUserMedia permissions for this origin are persisted only candidates from a single interface will be gathered in Chrome. -- from https://webrtc.github.io/samples/src/content/peerconnection/trickle-ice/

Just tested this, and on the current version, snapdrop can't work when VPN enabled on android, but it will work after given the audio/video permission