In r8605, DTLS is enabled by default for native webrtc. So we have to disable it explicitly in peerconnection example for loopback test.

BUG=4386
TEST=Manual Test
R=jiayl@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44599004

Cr-Commit-Position: refs/heads/master@{#8677}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8677 4adac7df-926f-26a2-2b94-8c16560cd09d