RTW_NEXT_IDX
next = RTW_NEXT_IDX(tdb, next)) {
next = RTW_NEXT_IDX(tdb, next);
next = RTW_NEXT_IDX(tdb, next), i++) {
i++, desc = RTW_NEXT_IDX(tdb, desc)) {
sizeof(struct rtw_txdesc) * RTW_NEXT_IDX((__htc), (__idx)))