MAX_QUEUE_MEMORY
dev->rx_qlen = MAX_QUEUE_MEMORY / dev->rx_urb_size;
dev->tx_qlen = MAX_QUEUE_MEMORY / dev->hard_mtu;
dev->rx_qlen = 5 * MAX_QUEUE_MEMORY / dev->rx_urb_size;
dev->tx_qlen = 5 * MAX_QUEUE_MEMORY / dev->hard_mtu;