Fraction lost statistics not being reported

A bug is causing fraction lost to always be set to zero when calling
ViERTP_RTCP::Get(Send|Receive)ChannelRtcpStatistics. Fix this and update
tests to catch it.

BUG=
R=holmer@google.com, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5219004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5235 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed