Raise streams for SetMaxSendBitrates above 2000k.

Fixes b=AS effectively not setting bitrates above 2000k.

BUG=1788,4469
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/47839004

Cr-Commit-Position: refs/heads/master@{#8882}
3 files changed