Calculate marking probability only on dequeue in DualPi2

This makes the sojourn time calculation more robust and matches the recommendation for how to calculate sojourn time in RFC 9332.

Note that to avoid starving classic queues - we should implement c_protection.

Bug: webrtc:447037083
Change-Id: Ib47cae83f455ad8dced79f4da826b28dfe478dd4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/419363
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Reviewed-by: Christoffer Dewerin <jansson@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#46008}