kernel: kmod-udptunnel6 depends on IPv6

Spotted a missing 'ip6_udp_tunnel.ko' build failure during a local
build with all kmods enabled but globally disabled IPv6 support.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

SVN-Revision: 47487

package/kernel/linux/modules/netsupport.mk

@@ -159,6 +159,7 @@ $(eval $(call KernelPackage,udptunnel4))
 define KernelPackage/udptunnel6
   SUBMENU:=$(NETWORK_SUPPORT_MENU)
   TITLE:=IPv6 UDP tunneling support
+  DEPENDS:=@IPV6
   KCONFIG:=CONFIG_NET_UDP_TUNNEL
   FILES:=$(LINUX_DIR)/net/ipv6/ip6_udp_tunnel.ko
   AUTOLOAD:=$(call AutoLoad,32,ip6_udp_tunnel)