usbcore: store each usb_device's level in the tree

This patch (as778) adds a field to struct usb_device to store the
device's level in the USB tree.  In itself this number isn't really
important.  But the overhead is very low, and in a later patch it will
be used for preventing bogus warnings from the lockdep checker.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/hub.c

@@ -2414,6 +2414,7 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
 		usb_set_device_state(udev, USB_STATE_POWERED);
 		udev->speed = USB_SPEED_UNKNOWN;
  		udev->bus_mA = hub->mA_per_port;
+		udev->level = hdev->level + 1;
 
 		/* set the address */
 		choose_address(udev);

include/linux/usb.h

@@ -348,6 +348,7 @@ struct usb_device {
 
 	unsigned short bus_mA;		/* Current available from the bus */
 	u8 portnum;			/* Parent port number (origin 1) */
+	u8 level;			/* Number of USB hub ancestors */
 
 	int have_langid;		/* whether string_langid is valid */
 	int string_langid;		/* language ID for strings */