lglaf.py: Fix "Resource busy" error

Detach kernel driver (cdc_acm) to avoid this error:

    usb.core.USBError: [Errno 16] Resource busy

Deliberately do not call attach_kernel_driver for the detached devices,
it is likely that the user runs lglaf multiple times. The user can
unplug and re-insert their device if they want to re-attach the kernel
driver.

lglaf.py

@@ -215,6 +215,10 @@ class USBCommunication(Communication):
                         "has a kernel driver claimed the interface?")
                 raise e
         for intf in cfg:
+            if self.usbdev.is_kernel_driver_active(intf.bInterfaceNumber):
+                _logger.debug("Detaching kernel driver for intf %d",
+                        intf.bInterfaceNumber)
+                self.usbdev.detach_kernel_driver(intf.bInterfaceNumber)
             if self._match_interface(intf):
                 self._set_interface(intf)
         assert self.ep_in