[Libdlo] DL vendor descriptor separate from config desc?

[Andrew Kephart]

During initialization, udlfb tries to pull a vendor-specific descriptor
(0x5F) from the DL device, but on my device that particular info is
embedded in the config descriptor.  Are there DL devices where that
descriptor is independent of the config descriptor?

Also, total_len (in dlfb_parse_vendor_descriptor) is declared u8, which
may mask usb_get_descriptor errors.

-andrew