Some libraries hooking into WebRTC still manage to have the conference mode
flag enabled on non screenshare sources resulting in a bad rate allocation.
Bug: webrtc:11310
Change-Id: Id5205affb562511eda40c460e380c105d8589c51
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/182003
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31965}