Base NACK on send codecs.

Addressing discrepancy where NACK used to be set from send codecs in
WebRtcVideoEngine(1), and before this change, from recv codecs in
WebRtcVideoEngine2. This should address that NACK might be sent even if
the remote side does not support it.

BUG=4626
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/53409004

Cr-Commit-Position: refs/heads/master@{#9171}
3 files changed