notification_driver is deprecated to driver

TrivialFix
https://review.openstack.org/#/c/249508/

Change-Id: I18599c7221272279dfc2e9f5b297af09faff5c3b
diff --git a/lib/neutron-legacy b/lib/neutron-legacy
index 692d5ea..9497a23 100644
--- a/lib/neutron-legacy
+++ b/lib/neutron-legacy
@@ -1072,7 +1072,7 @@
 }
 
 function _configure_neutron_ceilometer_notifications {
-    iniset $NEUTRON_CONF DEFAULT notification_driver messaging
+    iniset $NEUTRON_CONF oslo_messaging_notifications driver messaging
 }
 
 function _configure_neutron_lbaas {