One of the NetEq methods needs to be virtual.

BUG=
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/20449004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6099 4adac7df-926f-26a2-2b94-8c16560cd09d