Also added cluster id to paced_sender::Packet and set the cluster id of the probing packet that is about to be sent. BUG=webrtc:5859 R=danilchap@webrtc.org, stefan@webrtc.org Review URL: https://codereview.webrtc.org/1962303002 . Cr-Commit-Position: refs/heads/master@{#12718}