iptables: use -ffunction-sections, -fdata-sections and --gc-sections

git-svn-id: svn://svn.openwrt.org/openwrt@36680 3c298f89-4303-0410-b956-a3cf2f4a3e73
firewall3: update to git head

 * use libiptc and libxtables directly to manage ruleset, iptables-restore is unreliable and prone to race conditions
 * make ipset integration more reliable

git-svn-id: svn://svn.openwrt.org/openwrt@36681 3c298f89-4303-0410-b956-a3cf2f4a3e73