usb: gadget: f_ncm: Add OS descriptor support

To be able to use the default USB class drivers available in Microsoft
Windows, we need to add OS descriptors to the exported USB gadget to
tell the OS that we are compatible with the built-in drivers.

Copy the OS descriptor support from f_rndis into f_ncm. As a result,
using the WINNCM compatible ID, the UsbNcm driver is loaded on
enumeration without the need for a custom driver or inf file.

Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/function/u_ncm.h

@@ -20,6 +20,9 @@ struct f_ncm_opts {
 	struct net_device		*net;
 	bool				bound;
 
+	struct config_group		*ncm_interf_group;
+	struct usb_os_desc		ncm_os_desc;
+	char				ncm_ext_compat_id[16];
 	/*
 	 * Read/write access to configfs attributes is handled by configfs.
 	 *