ugen: fix USB_IFACE_DRIVER_ACTIVE after detaching a driver

[avg]

Summary

Previosuly, USB_IFACE_DRIVER_ACTIVE would report that the driver is
active even after it detached. That's because a device(9) still
remains.

So, add device_is_alive(9) check for more accurate reporting.

[markj]

Seems reasonable to me.

sys/dev/usb/usb_generic.c

2383

Is there a reason not to use device_is_attached()? That seems closer to the spirit of this ioctl, but I'm not very familiar with this area.

[avg]

sys/dev/usb/usb_generic.c

2383

It was what I used initially, based on ugen_get_iface_driver.
But then I got a bit worried about concurrent probing and attaching, I decided to err on the side of caution.
Both checks worked equally well in my case.
BTW, the situation was this:

• connect a USB device
• see it claimed by uhid driver
• see that it is impossible to use with a libusb-based application
• unload uhid module
• the application still refuses to work because of USB_IFACE_DRIVER_ACTIVE

[markj]

sys/dev/usb/usb_generic.c

2383

That makes sense, thanks.