Remove ViENetwork usage in VideoSendStream.

Replaces interface usage with direct calls on ViEEncoder and ViEChannel
removing a layer of indirection.

BUG=1695
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/50809004

Cr-Commit-Position: refs/heads/master@{#9096}
2 files changed