Fix video_replay tool to respect RTX stream and fix default parameters.

Defaults are consistent with these used in CallTest.

BUG=none

Review-Url: https://codereview.webrtc.org/2972423002
Cr-Original-Commit-Position: refs/heads/master@{#18961}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 863f03ba38f397c078931d2bd27d40a4d60efc02