cmd/cli: ignore un-usable interfaces on darwin

So multi interfaces config won't emit un-necessary errors if the network
cable adapters are not being used on MacOS.

cmd/cli/os_windows.go

@@ -26,6 +26,12 @@ var (
 	resetDNSOnce sync.Once
 )
 
+// setDnsIgnoreUnusableInterface likes setDNS, but return a nil error if the interface is not usable.
+func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) error {
+	return setDNS(iface, nameservers)
+}
+
+// setDNS sets the dns server for the provided network interface
 func setDNS(iface *net.Interface, nameservers []string) error {
 	if len(nameservers) == 0 {
 		return errors.New("empty DNS nameservers")