usb-device: Default bDeviceClass, bDeviceSubClass, bDeviceProtocol to 0.

These values are apparently interpreted as "interface defined", which is
a good fit for what happens here (more than one interface might show up in
the device).

It works as expected for the examples in Linux and Windows 10. There will
probably be some scenarios where a different value needs to be explicitly
passed in for the device.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

micropython/usb/usb-device/usb/device/impl.py

@@ -95,9 +95,9 @@ class _Device:
         id_vendor=None,
         id_product=None,
         bcd_device=None,
-        device_class=None,
-        device_subclass=None,
-        device_protocol=None,
+        device_class=0,
+        device_subclass=0,
+        device_protocol=0,
         config_str=None,
         max_power_ma=None,
     ):
@@ -137,9 +137,9 @@ class _Device:
             f[0],  # bLength
             f[1],  # bDescriptorType
             f[2],  # bcdUSB
-            maybe_set(device_class, 3),  # bDeviceClass
-            maybe_set(device_subclass, 4),  # bDeviceSubClass
-            maybe_set(device_protocol, 5),  # bDeviceProtocol
+            device_class,  # bDeviceClass
+            device_subclass,  # bDeviceSubClass
+            device_protocol,  # bDeviceProtocol
             f[6],  # bMaxPacketSize0, TODO: allow overriding this value?
             maybe_set(id_vendor, 7),  # idVendor
             maybe_set(id_product, 8),  # idProduct