This change fixes some inefficiencies and quirks in the code that originates in RtpTransport leading up to the demux. This work is in preparation for more refactoring of the Demux stage onwards. Bug: webrtc:10297 Change-Id: I7b8f00134657d62c722939618a55a91a2b6040bd Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128220 Commit-Queue: Amit Hilbuch <amithi@webrtc.org> Reviewed-by: Steve Anton <steveanton@webrtc.org> Reviewed-by: Seth Hampson <shampson@webrtc.org> Cr-Commit-Position: refs/heads/master@{#27185}