Add functions to ViE API to enable/disable the absolute send time header extension.

BUG=
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1487004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4065 4adac7df-926f-26a2-2b94-8c16560cd09d
7 files changed