fix build failure when no network interfaces are available. On buildd systems using sbuild chroot mode unshare, the network interface leading to Internet is not exposed. However the default construction method for instantiating Net::Frame::Devices relies on the existence of a network interface able to route to 1.1.1.1. This change adjusts the test suite items failing when not such interfaces are available, by trying to refer to loopback interfaces instead. Note this slightly changes the meaning of the t/04-new-default.t, as it does not test the default behavior anymore, but it tests the behavior with ipv6 targets instead. . This addresses a Debian infrastructure specific behavior, probably not much worth forwarding upstream.
