Detect enabling or disabling of VPN on Android so
NetworkChangeNotifierAndroid can send out the proper notifications.
This detection uses an instantiation of the AddressTrackerLinux to
listen for NETLINK messages from the kernel about tunnel interaces.

BUG=318794

Review URL: https://codereview.chromium.org/134873015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249991 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249991