This avoid sending more padding than required for the current target
constraints.
Bug: webrt:8415
Change-Id: I3a668990f026414ab78f8406248cde18b81123cc
Reviewed-on: https://webrtc-review.googlesource.com/77763
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23364}