qubes/app: fix notifying about default_netvm change

Notify every VM that is affected, not only those providing network
itself.

qubes/app.py

@@ -1087,7 +1087,7 @@ class Qubes(qubes.PropertyHolder):
             oldvalue=None):
         # pylint: disable=unused-argument
         for vm in self.domains:
-            if vm.provides_network and vm.property_is_default('netvm'):
+            if vm.property_is_default('netvm'):
                 # fire property-del:netvm as it is responsible for resetting
                 # netvm to it's default value
                 vm.fire_event('property-del:netvm',