Gateway Patchpack #1

-[util.inc] is_linklocal($ipaddr) is now fully LL aware for both ipv4 and ipv6;
-[util.inc] Added is_valid_iface_ipaddrv4($ipaddr) and is_valid_iface_ipaddrv6($ipaddr) to check if given $ipaddr can be actually used on interface;
-[filter.inc] filter_generate_user_rule($rule). Add missing gettext;
-[gwlb.inc] Don't create dynamic gateways for ifaces without IP address;
-[gwlb.inc] Don't monitor dynamic gateway with an invalid IP address by default;