usb: gadget: Kconfig: Fix configfs-based RNDIS function build

USB_CONFIGFS_RNDIS depends on USB_U_RNDIS. Select it.
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/Kconfig

@@ -639,6 +639,7 @@ config USB_CONFIGFS_RNDIS
 	depends on USB_CONFIGFS
 	depends on NET
 	select USB_U_ETHER
+	select USB_U_RNDIS
 	select USB_F_RNDIS
 	help
 	   Microsoft Windows XP bundles the "Remote NDIS" (RNDIS) protocol,