similar to what is done for FID and FEC-FR but SIM can have more than
one secondary SSRC.
BUG=chromium:1477075
Change-Id: I4c9b4feaa421f53e424fc17bfc9ee2c185c68fb0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/318520
Reviewed-by: Sergey Silkin <ssilkin@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40679}