kirkwood: disable image for Linksys EA3500 (Audi)

Due to the switch to DSA, the kernel image has become too big (2641k) for the
kernel partition (2624k) on this device:

  WARNING: Image file [...]/linux-kirkwood/linksys_audi-uImage is too big

Disable the device until this is fixed, so buildbots can continue their work.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/kirkwood/image/Makefile

@@ -91,6 +91,7 @@ define Device/linksys_audi
   UBINIZE_OPTS := -E 5
   IMAGE/factory.bin := append-kernel | pad-to $$$$(KERNEL_SIZE) | append-ubi
   BOARD_NAME := linksys-audi
+  DEFAULT := n
 endef
 TARGET_DEVICES += linksys_audi