gio/tests/network-address: fix for systems with large ifindexes

In some virtualization setups, ifindexes can end up becoming very
large, and so the existing code that assumes that *some* interface
must have an index less than 255 fails.

Fix this by explicitly looking for "lo" first. And then if that fails
(on Windows, or other systems where the loopback interface is not
called "lo"), try indexes up to 1024 rather than 255.

https://bugzilla.gnome.org/show_bug.cgi?id=723048