…transfer

is called on one transfer, all transfers on the same endpoint are
cancelled. Calling libusb_cancel_transfer on additional transfers on the
same endpoint _may_ result in macOS returning kIOReturnAborted. The net
result is the bladeRF can no longer be communicated with.

The fix to this is to only call libusb_cancel_transfer once in
cancel_all_transfers and set the appropriate state for all transfers.
Refer to libusb_cancel_transfer documentation for more details.