Handle correctly interface_num in USB host API

[xluciano]

In the the USB host API used for libusb-1.0 we have

control_ret_t control_init_usb(int vendor_id, int product_id, int interface_num)

but interface_num is disregarded and the first interface with the correct Vendor and Product ID's is used. This is not correct, since it won't work if the requested interface is not the first in the descriptors list.

The interface number is correctly used for the libusb-win32 API used in Windows.