Dynamically select emulated device speed

[xairy]

The proxy currently always uses USB_SPEED_HIGH for emulating devices.

We need to dynamically figure out the actual speed of the device via libusb_get_device_speed and use that for usb_raw_init.

We then also need to improve #10 to patch in the right bMaxPacketSize0 depending on the used speed. Note that the speed provided to usb_raw_init is merely a hint, and the UDC might decide to use a different one. To find out which speed UDC decided to use, we need to resolve xairy/raw-gadget#41 first.

Not a critical issue, filing to not forget.

[AristoChen]

Hi,

Thanks for opening this issue, I was aware of the speed issue when I was drafting the code 2 years ago. However, it was not recoreded anywhere so apparently I forgot it, thanks for reminding me!