since the extension can be too large to fit the 16 bytes available
to one-byte extensions
https://www.rfc-editor.org/rfc/rfc8285#section-4.2
when including the width and height fields.
Also document when those fields are sent.
BUG=webrtc:12000
Change-Id: If17f57d40c0bde9b060f223c548e407d6c124b82
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/321200
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Commit-Queue: Philipp Hancke <phancke@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#40910}
dde1cb6212