Hi, net-firewall/iptables-1.4.2-r1 needlessly inherits the linux-info eclass, requiring kernel sources to be available when in fact compilation works without them. Simply removing the "linux-info" token from the inherit line in the ebuild allows the package to be built correctly without the kernel sources being present. No functions from linux-info.eclass are used by the ebuild.
When the l7filters stuff is updated for 1.4.2 or newer, linux-info will be needed again, however vapier can probably decided if we just take it out for now.
the guys maintaining the filters are slow in updating, so we'll just roll with it http://sources.gentoo.org/net-firewall/iptables/iptables-1.4.2-r1.ebuild?r1=1.2&r2=1.3