Default destination used by c line should be IPv4 only to avoid parsing error in legacy client.

Make sure the IP family overwrites the preference of candidates. Also,
make sure only UDP is used as default destination.

BUG=4269
R=juberti@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/36009004

Cr-Commit-Position: refs/heads/master@{#8258}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8258 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed