First incoming packet was not accounted for in receive stats. Changed call order for incoming packet to receive statistics class.
Receive stats is reset if the payload type changes. Update stats after a possible reset.

R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12549004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6247 4adac7df-926f-26a2-2b94-8c16560cd09d