optimizing for the fairly common case of many recv-only
mediasections.
BUG=webrtc:14808
Change-Id: Iae68c5bb7a5516d77f908f1effbb50a5ed750f92
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/290984
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39122}