kmod-sched-cake: do not build on kernel 3.18

kmod-sched-cake does not build on kernel 3.18, so add the dependency to
not even try.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

package/kernel/kmod-sched-cake/Makefile

@@ -26,7 +26,7 @@ define KernelPackage/sched-cake
   URL:=https://github.com/dtaht/sch_cake
   FILES:=$(PKG_BUILD_DIR)/sch_cake.ko
   AUTOLOAD:=$(call AutoLoad,75,sch_cake)
-  DEPENDS:=+kmod-ipt-conntrack
+  DEPENDS:=+kmod-ipt-conntrack @!LINUX_3_18
 endef
 
 include $(INCLUDE_DIR)/kernel-defaults.mk