usb: gadget: add RNDIS configfs options for class/subclass/protocol

This adds 3 new options to the RNDIS gadget function configs. It allows
overriding the default USB interface class/subclass/protocol.

The motivation for this is that if you set the values to "ef" (Misc),
"04" (RNDIS), "01" (Ethernet) respectively, then the device will be
recognized by the rndiscmp.inf file in Windows Vista and newer and will
cause Windows to load the correct RNDIS driver without the need for a
custom (signed) .inf file.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
diff --git a/Documentation/ABI/testing/configfs-usb-gadget-rndis b/Documentation/ABI/testing/configfs-usb-gadget-rndis
index e32879b..1373990 100644
--- a/Documentation/ABI/testing/configfs-usb-gadget-rndis
+++ b/Documentation/ABI/testing/configfs-usb-gadget-rndis
@@ -12,3 +12,6 @@
 				Ethernet over USB link
 		dev_addr	- MAC address of device's end of this
 				Ethernet over USB link
+		class		- USB interface class, default is 02 (hex)
+		subclass	- USB interface subclass, default is 06 (hex)
+		protocol	- USB interface protocol, default is 00 (hex)