usbip: move usbip kernel code out of staging

At this point, USB/IP kernel code is fully functional
and can be moved out of staging.

Signed-off-by: Valentina Manea <valentina.manea.m@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/Kconfig b/drivers/usb/Kconfig
index e0cad44..cf1b19b 100644
--- a/drivers/usb/Kconfig
+++ b/drivers/usb/Kconfig
@@ -92,6 +92,8 @@
 
 source "drivers/usb/image/Kconfig"
 
+source "drivers/usb/usbip/Kconfig"
+
 endif
 
 source "drivers/usb/musb/Kconfig"