ath79: Deactivate ZyXEL NBG6716 by default

The kernel image is too big now and the build fails.

WARNING: Image file zyxel_nbg6716-kernel.bin is too big: 4205404 > 4194304

Signed-off-by: Hauke Mehrtens <[email protected]>

target/linux/ath79/image/nand.mk

@@ -256,5 +256,6 @@ define Device/zyxel_nbg6716
   IMAGE/factory.bin := append-kernel | pad-to $$$$(KERNEL_SIZE) | append-ubi | \
 	zyxel-factory
   UBINIZE_OPTS := -E 5
+  DEFAULT := n
 endef
 TARGET_DEVICES += zyxel_nbg6716