Also moves and simplifies SetSendCodec from VideoSendStream to mostly inside ViEEncoder. This is necessary for making ReconfigureVideoEncoder asynchronous as we don't post any result back. BUG=webrtc:5494 R=stefan@webrtc.org TBR=mflodman@webrtc.org Review URL: https://codereview.webrtc.org/1754283002 . Cr-Commit-Position: refs/heads/master@{#11847}