replication-slave ha policy displays wrong default value for allow-failback

Issue

• Wrong value for the default allow-failback attribute:

• Default value for allow-failback shows true instead false:

  /profile=backup/subsystem=messaging-activemq/server=default/ha-  policy=replication-slave:read-resource(recursive=true,include-runtime=true,include-defaults=true)
  {
      "outcome" => "success",
      "result" => {
          "allow-failback" => true,
          "cluster-name" => "my-cluster",
          "group-name" => expression "${backup-group}",
          "initial-replication-sync-timeout" => 30000L,
          "max-saved-replicated-journal-size" => 250,
          "restart-backup" => true,
          "scale-down" => undefined,
          "scale-down-cluster-name" => undefined,
          "scale-down-connectors" => undefined,
          "scale-down-discovery-group" => undefined,
          "scale-down-group-name" => undefined
    }
  }