Use the configured remote ssrc instead of relying on the first received packet RtpStreamReceiver.

This solves an issue where if the first packet happens to be an RTX packet, it is recovered with an incorrect SSRC.

BUG=webrtc:5654

Review-Url: https://codereview.webrtc.org/2928123002
Cr-Original-Commit-Position: refs/heads/master@{#18512}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: b4ab381ce372f065b003cac925d10b34d978da71
2 files changed