6to4: update OpenWrt documentation URL

Signed-off-by: Vieno Hakkerinen <txt.file@txtfile.eu>

package/network/ipv6/6to4/Makefile

@@ -25,7 +25,7 @@ endef
 
 define Package/6to4/description
 Provides support for 6to4 tunnels in /etc/config/network.
-Refer to http://wiki.openwrt.org/doc/uci/network for
+Refer to https://openwrt.org/docs/guide-user/base-system/basic-networking
 configuration details.
 endef