Add a memcheck exclusion for EndToEndTest.CanSwitchToUseAllSsrcs.

TBR=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/29899004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7502 4adac7df-926f-26a2-2b94-8c16560cd09d