Revert "Revert of Update the BWE when the network route changes. (patchset #5 id:180001 of https://codereview.webrtc.org/2000063003/ )"

This reverts commit 72d41aa6da94dacb8a8464d1abd4ca7d1afffc65.

New change made:
Do not reset the BWE when the new network route is not ready to send media.

BUG=
R=pthatcher@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2041593002 .

Cr-Original-Commit-Position: refs/heads/master@{#13280}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 5b5d2cdad7018993272525a723ef34f7da5c45f2
15 files changed