rb532: increase kernel size limit

This is required to support kernel 4.9.

Signed-off-by: Roman Yeryomin <roman@advem.lv>
[rewrite commit message (subject <= 50 characters)]
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

target/linux/rb532/image/Makefile

@@ -85,7 +85,7 @@ define Image/Build
 	$(CP) $(KDIR)/vmlinux.elf $(BIN_DIR)/$(IMG_PREFIX)-$(1).kernel
 	$(STAGING_DIR_HOST)/bin/patch-cmdline $(BIN_DIR)/$(IMG_PREFIX)-$(1).kernel 'root=/dev/sda2 '
 	./gen_image.sh $(BIN_DIR)/$(IMG_PREFIX)-combined-$(1).bin \
-		5 $(BIN_DIR)/$(IMG_PREFIX)-$(1).kernel \
+		6 $(BIN_DIR)/$(IMG_PREFIX)-$(1).kernel \
 		$(CONFIG_TARGET_ROOTFS_PARTSIZE) $(KDIR)/root.$(1) \
 		128
 endef