A reset of Bwe and rates on network route change triggers
switching of the RemoteBitrateEstimator from DelayBasedBwe
to RemoteBitrateEstimatorAbsSendTime. This is unexpected,
fix this.
BUG=
R=stefan@webrtc.org
Review URL: https://codereview.webrtc.org/2193043002 .
Cr-Commit-Position: refs/heads/master@{#13594}