MDL-48701 inbound: Use correct method in invalid email handler

Invalid email handler doesn't allow alteration in validate sender config. Make sure this is reflected in the UI as well

admin/tool/messageinbound/classes/message/inbound/invalid_recipient_handler.php

@@ -46,7 +46,7 @@ class invalid_recipient_handler extends \core\message\inbound\handler {
     /**
      * Do not allow changes to the address validation setting.
      */
-    public function allow_validateaddress_change() {
+    public function can_change_validateaddress() {
         return false;
     }