idpf_tx_buf_next
while (idpf_tx_buf_next(tx_buf) != IDPF_TXBUF_NULL) {
buf_id = idpf_tx_buf_next(tx_buf);
while (idpf_tx_buf_next(tx_buf) != IDPF_TXBUF_NULL) {
tx_buf = &txq->tx_buf[idpf_tx_buf_next(tx_buf)];
idpf_tx_buf_next(tx_buf) = IDPF_TXBUF_NULL;
idpf_tx_buf_next(tx_buf) = IDPF_TXBUF_NULL;
idpf_tx_buf_next(tx_buf) = next_buf_id;
idpf_tx_buf_next(tx_buf) = IDPF_TXBUF_NULL;