sip: set unidirection transaction flag

rust/src/sip/sip.rs

@@ -392,7 +392,7 @@ pub unsafe extern "C" fn rs_sip_register_parser() {
         get_tx_iterator: None,
         get_tx_data: rs_sip_get_tx_data,
         apply_tx_config: None,
-        flags: 0,
+        flags: APP_LAYER_PARSER_OPT_UNIDIR_TXS,
         truncate: None,
     };