Set local SSRC for VideoReceiveStream. As a bonus, also removes GenerateRandomSsrc, which only worked on sender configs. There's no point to generate random SSRCs in tests. BUG=2691 R=mflodman@webrtc.org, stefan@webrtc.org Review URL: https://webrtc-codereview.appspot.com/4689004 git-svn-id: http://webrtc.googlecode.com/svn/trunk@5201 4adac7df-926f-26a2-2b94-8c16560cd09d