Fix regression where script crashes when using IPv6

Regression was introduced in d67aadd038

genconfdrv/genconfdrv.py

@@ -312,7 +312,10 @@ def main():
         cfgdrv.set_hostname(args.hostname)
 
         for net in args.networks:
-            net = net.split(":")
+            if ";" in net:
+                net = net.split(";")
+            else:
+                net = net.split(":")
             cfgdrv.conf_network(*net)
 
         if args.nameservers: