Fix customConstructor to work correctly with newargs

mininet/util.py

@@ -551,6 +551,7 @@ def customConstructor( constructors, argStr ):
             params.update( kwargs )
             if not newargs:
                 cls.__init__( self, name, *args, **params )
+                return
             if args:
                 warn( 'warning: %s replacing %s with %s\n' %
                       ( constructor, args, newargs ) )