`remote_ssrc` can be considered const while some other state represented by rtp_config() can not and also is tied to a specific thread. Separating access to these variables, makes moving things around easier. Bug: webrtc:11993 Change-Id: I70aa000daab6174a401e01dca163213174e8f284 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261316 Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/main@{#36818}