conntrack: enable support for netfilter conntrack zones

Storage of such zones is provided by a nf_ct_ext struct, hence conntrack
memory foot print will not be increased if zones are not used.

Signed-off-by: Alin Năstac <alin.nastac@gmail.com>

package/kernel/linux/modules/netfilter.mk

@@ -68,6 +68,7 @@ define KernelPackage/nf-conntrack
   KCONFIG:= \
         CONFIG_NETFILTER=y \
         CONFIG_NETFILTER_ADVANCED=y \
+        CONFIG_NF_CONNTRACK_ZONES=y \
 	$(KCONFIG_NF_CONNTRACK)
   FILES:=$(foreach mod,$(NF_CONNTRACK-m),$(LINUX_DIR)/net/$(mod).ko)
   AUTOLOAD:=$(call AutoProbe,$(notdir $(NF_CONNTRACK-m)))