Using RTX SSRCs and payload type for retransmission of video. This corresponds to the behavior when using the peer connection API. Bug: webrtc:9883 Change-Id: Ic0e3964d097f42219ca225513a4bc771d70ccaa4 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/164460 Commit-Queue: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Cr-Commit-Position: refs/heads/master@{#30248}