When layers are activated/deactivated via UpdateActiveSimulcastLayers, the flag wasn't being updated. This resulted in calls to Stop() getting ignored after an implicit start via activating layers. Bug: chromium:1234779 Change-Id: I4a72e624874526d27d3e97d6903112367c5e77fb Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227700 Reviewed-by: Magnus Flodman <mflodman@webrtc.org> Commit-Queue: Tommi <tommi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34654}