Limit disabling of PeerConnectionEndToEndTest.Call to Windows

The test seems to be flaky only on Windows.

BUG=4464
TBR=kjellander@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44829004

Cr-Commit-Position: refs/heads/master@{#8835}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8835 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed