ReportBlock is the the real receiver report.
Triggering rtt update on ReportBlock support clients that send receiver
report blocks attached to SenderReport rather than ReceiverReport.
Bug: webrtc:7996
Change-Id: Ie826fa09fd1bf0e5256e995649f66811b5192761
Reviewed-on: https://webrtc-review.googlesource.com/4040
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20014}