ipq40xx: reenable Zyxel NBG6617 by default

The Zyxel NBG6617 already uses lzma to compress the kernel.
A local build with every module enabled (either as =Y or =M)
ended produced a 3058 KiB kernel (the kernel partition is 4MiB).
It booted just fine, let's reenable the device.

Signed-off-by: Christian Lamparter <[email protected]>

target/linux/ipq40xx/image/generic.mk

@@ -906,7 +906,6 @@ define Device/zyxel_nbg6617
 	IMAGE/factory.bin := append-rootfs | pad-rootfs | pad-to 64k | check-size $$$$(ROOTFS_SIZE) | zyxel-ras-image separate-kernel
 	IMAGE/sysupgrade.bin/squashfs := append-rootfs | pad-rootfs | check-size $$$$(ROOTFS_SIZE) | sysupgrade-tar rootfs=$$$$@ | append-metadata
 	DEVICE_PACKAGES := kmod-usb-ledtrig-usbport
-	DEFAULT := n
 endef
 TARGET_DEVICES += zyxel_nbg6617