routes: generate routes also without IP (bnc#895219)

When there is a device route in ifroute file and were able to assign the routes to an interface, e.g.:
   192.168.0.1/32 -                        - eth0
   192.168.0.0/16  192.168.0.1/32 - -
just generate the routes and do not enforce, that there is also some static address assigned.