USB: Allow usbmon as a module even if usbcore is builtin

usbmon can only be built as a module if usbcore is a module too. Trivial
changes to the relevant Kconfig and Makefile (and a few trivial changes
elsewhere) allow usbmon to be built as a module even if usbcore is
builtin.

This is verified to work in all 9 permutations (3 correctly prohibited
by Kconfig, 6 build a suitable result).

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/mon/Kconfig

@@ -3,14 +3,13 @@
 #
 
 config USB_MON
-	bool "USB Monitor"
-	depends on USB!=n
-	default y
+	tristate "USB Monitor"
+	depends on USB
+	default y if USB=y
+	default m if USB=m
 	help
-	  If you say Y here, a component which captures the USB traffic
+	  If you select this option, a component which captures the USB traffic
 	  between peripheral-specific drivers and HC drivers will be built.
 	  For more information, see <file:Documentation/usb/usbmon.txt>.
 
-	  This is somewhat experimental at this time, but it should be safe.
-
-	  If unsure, say Y.
+	  If unsure, say Y (if allowed), otherwise M.

drivers/usb/mon/Makefile

@@ -4,5 +4,4 @@
 
 usbmon-objs	:= mon_main.o mon_stat.o mon_text.o mon_bin.o mon_dma.o
 
-# This does not use CONFIG_USB_MON because we want this to use a tristate.
-obj-$(CONFIG_USB)	+= usbmon.o
+obj-$(CONFIG_USB_MON)	+= usbmon.o