atusb.c: add spaced around + and -
atusb.h: salvage cute explanation of 0x1540 from usb-ids.h
atusb.c: temporarily add massive resubmit delay and have only one in-flight RX URB

This means that we see up to three or four frames per burst:

1. the first one, for the pending RX URB
2. the second one, that gets stored in the device's USB buffer, waiting
   for the URB to be resubmitted
3. the third one, that gets stored in the firmware's RX buffer, waiting
   for the URB to be resubmitted again

Without queued_rx in the firmware, the following TRX_END interrupts
are ignored. Firmware versions with queued_rx will send one more frame.

If we don't enable dynamic buffer protection:

4. the last one, that has overwritten its predecessors in the
   transceiver buffer

If we do enable dynamic buffer protection (untested):

4. the fourth one, that gets stored in the transceiver buffer and is
   protected until retrieval

Note that without queued_rx, buffer dynamic protection would cause the
receiver to stall in a burst since we'd lose the last TRX_END interrupt,
thus never retrieve the frame and therefore never release the protection.
atusb.c: enable dynamic buffer protection
atusb: send ACK sequence number with ATUSB_TX