Add a new class InterfaceAddress inherited from IPAddress to keep track of IPv6 Address flags.

Skeleton put in place in Network::GetFilterIPs() which will be used to
filter addresses

BUG=3773
R=jiayl@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/23439004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7126 4adac7df-926f-26a2-2b94-8c16560cd09d