FW_TXDESC_GETFIELD_1
ctrl = FW_TXDESC_GETFIELD_1(sc, buf, f_tx_ctrl);
error = FW_TXDESC_GETFIELD_1(sc, buf, f_tx_error);
ntries = FW_TXDESC_GETFIELD_1(sc, buf, f_tx_rts_fail) +
FW_TXDESC_GETFIELD_1(sc, buf, f_tx_ack_fail);
ctrl = FW_TXDESC_GETFIELD_1(sc, txbuf, f_tx_ctrl);