ntp: set unidirection transaction flag

rust/src/ntp/ntp.rs

@@ -406,7 +406,7 @@ pub unsafe extern "C" fn rs_register_ntp_parser() {
         get_tx_iterator    : None,
         get_tx_data        : rs_ntp_get_tx_data,
         apply_tx_config    : None,
-        flags              : 0,
+        flags              : APP_LAYER_PARSER_OPT_UNIDIR_TXS,
         truncate           : None,
     };