Firewall network validation is different than in metal-networker

[majst01]

Its possible to allocate a firewall which leads to a failure during installation:

{"level":"panic","ts":1637767309.1289444,"caller":"cmd/root.go:93","msg":"expectation at least one public network (private: false, underlay: false) is present failed","stacktrace":"github.com/metal-stack/metal-networker/cmd.configure\n\tgithu
b.com/metal-stack/metal-networker/cmd/root.go:93\ngithub.com/metal-stack/metal-networker/cmd.glob..func1\n\tgithub.com/metal-stack/metal-networker/cmd/firewall.go:24\ngithub.com/spf13/cobra.(*Command).execute\n\tgithub.com/spf13/cobra@v1.1.3/
command.go:852\ngithub.com/spf13/cobra.(*Command).ExecuteC\n\tgithub.com/spf13/cobra@v1.1.3/command.go:960\ngithub.com/spf13/cobra.(*Command).Execute\n\tgithub.com/spf13/cobra@v1.1.3/command.go:897\ngithub.com/metal-stack/metal-networker/cmd.
Execute\n\tgithub.com/metal-stack/metal-networker/cmd/root.go:43\nmain.main\n\tgithub.com/metal-stack/metal-networker/main.go:6\nruntime.main\n\truntime/proc.go:225"}                                                                            
panic: expectation at least one public network (private: false, underlay: false) is present failed