Fix USB descriptors for Windows

teensy4/usb_desc.c

 #define LSB(n) ((n) & 255)
 #define MSB(n) (((n) >> 8) & 255)
 
+#ifdef CDC_IAD_DESCRIPTOR
+#ifndef DEVICE_CLASS
+#define DEVICE_CLASS 0xEF
+#endif
+#ifndef DEVICE_SUBCLASS
+#define DEVICE_SUBCLASS 0x02
+#endif
+#ifndef DEVICE_PROTOCOL
+#define DEVICE_PROTOCOL 0x01
+#endif
+#endif
+
+
 // USB Device Descriptor.  The USB host reads this first, to learn
 // what type of device is connected.
 static uint8_t device_descriptor[] = {
         4,                                      // bDescriptorType
         EXPERIMENTAL_INTERFACE,                 // bInterfaceNumber
         0,                                      // bAlternateSetting
-        1,                                      // bNumEndpoints
+        2,                                      // bNumEndpoints
         0xFF,                                   // bInterfaceClass (0xFF = Vendor)
         0x6A,                                   // bInterfaceSubClass
         0xFF,                                   // bInterfaceProtocol
         4,                                      // bDescriptorType
         EXPERIMENTAL_INTERFACE,                 // bInterfaceNumber
         0,                                      // bAlternateSetting
-        1,                                      // bNumEndpoints
+        2,                                      // bNumEndpoints
         0xFF,                                   // bInterfaceClass (0xFF = Vendor)
         0x6A,                                   // bInterfaceSubClass
         0xFF,                                   // bInterfaceProtocol

teensy4/usb_desc.h

 #if defined(USB_SERIAL)
   #define VENDOR_ID		0x16C0
   #define PRODUCT_ID		0x0483
-  #define DEVICE_CLASS		2	// 2 = Communication Class
   #define MANUFACTURER_NAME	{'T','e','e','n','s','y','d','u','i','n','o'}
   #define MANUFACTURER_NAME_LEN	11
   #define PRODUCT_NAME		{'U','S','B',' ','S','e','r','i','a','l'}
   #define EP0_SIZE		64
   #define NUM_ENDPOINTS		4
   #define NUM_USB_BUFFERS	12
-  #define NUM_INTERFACE		3
+  #define NUM_INTERFACE		2
+  #define CDC_IAD_DESCRIPTOR    1       // Serial
   #define CDC_STATUS_INTERFACE	0
   #define CDC_DATA_INTERFACE	1
   #define CDC_ACM_ENDPOINT	2
   #define CDC_TX_SIZE_480       512
   #define CDC_RX_SIZE_12        64
   #define CDC_TX_SIZE_12        64
-  #define EXPERIMENTAL_INTERFACE 2
+  //#define EXPERIMENTAL_INTERFACE 2
   #define ENDPOINT2_CONFIG	ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_INTERRUPT
   #define ENDPOINT3_CONFIG	ENDPOINT_RECEIVE_BULK + ENDPOINT_TRANSMIT_UNUSED
   #define ENDPOINT4_CONFIG      ENDPOINT_RECEIVE_UNUSED + ENDPOINT_TRANSMIT_BULK