Add SSRC to RtpEncodingParameters for audio.

Was added for video initially, but not for audio.

BUG=webrtc:6862

Review-Url: https://codereview.webrtc.org/2568553002
Cr-Original-Commit-Position: refs/heads/master@{#15552}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cb44343006c1fcf282ae3ce55640ba297be2ad74
2 files changed