Resolve issue with usb_relay_device_open_with_serial_number (orig. lib)

[pavel-a]

I don't understand what this function should return: the low -level handle or struct usb_relay_device_info *. If the former, how to get the info (number of relays, etc.) from this handle.

Currently in my lib the handle is same as usb_relay_device_info * but this may change later?
I'd like this f() to publicly return the struct ptr, or add another f() because I need to know at least the number of relays.

In original package the command util uses only usb_relay_device_open_with_serial_number and the GUI uses only usb_relay_device_enumerate and usb_relay_device_open.