The stub libusb library used for testing writes the control request to a
dump file. By default, this file is block-buffered, and on a typical
Linux system, it waits until it receives about a page worth of data
before flushing it to disk. This results in a delay in monitoring
packets when running a debug program.
This change makes the file line-buffered instead, which results in the
debug output for every single packet getting flushed to disk without
having to wait for a full page of data.
With the release of libusb 1.0.22, `libusb_set_debug` has been
deprecated and replaced by `libusb_set_option`. This function is a new
generic API to add additional functionality in the future without having
to introduce new functions.
This change checks for `LIBUSB_API_VERSION` of at least `0x01000106`,
which is the version corresponding to 1.0.22, and if it matches, it
replaces the calls to `libusb_set_debug` with equivalent calls to
`libusb_set_option`.
nirenjan