Support for ifroute

bnc#897394, bnc#866250
This is wrong: it skips writing the global routes if we haven't found any. But instead it should write an empty list (to remove any previously configured global routes), which is actually implemented by writing an empty string, as seen above, referencing [bug 4476](https://bugzilla.novell.com/show_bug.cgi?id=suse4476)(!). That code should be moved here.