zabbix: enable IPv6 support

compile tested on trunk, run tested on CC (ar71xx)

size before:
 96757 zabbix-agentd_2.4.6-1_ar71xx.ipk
 29180 zabbix-get_2.4.6-1_ar71xx.ipk
258979 zabbix-proxy_2.4.6-1_ar71xx.ipk
 35121 zabbix-sender_2.4.6-1_ar71xx.ipk
282885 zabbix-server_2.4.6-1_ar71xx.ipk

size after:
 97359 zabbix-agentd_2.4.6-2_ar71xx.ipk
 29841 zabbix-get_2.4.6-2_ar71xx.ipk
259948 zabbix-proxy_2.4.6-2_ar71xx.ipk
 35801 zabbix-sender_2.4.6-2_ar71xx.ipk
284019 zabbix-server_2.4.6-2_ar71xx.ipk

original PR by Thomas Bahn <thomas-bahn@gmx.net>

Signed-off-by: Etienne CHAMPETIER <champetier.etienne@gmail.com>

admin/zabbix/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=zabbix
 PKG_VERSION:=2.4.6
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=@SF/zabbix
@@ -107,6 +107,7 @@ CONFIGURE_ARGS+= \
 	--enable-agent \
 	--enable-server \
 	--enable-proxy \
+	$(call autoconf_bool,CONFIG_IPV6,ipv6) \
 	--disable-java \
 	--with-sqlite3="$(STAGING_DIR)/usr"