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>

diff --git a/include/linux/usb.h b/include/linux/usb.h
index c663032..df5c93e 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -348,6 +348,7 @@
 
 	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 */