I recently upgraded an old server from gentoo-sources-2.4.20 to gentoo-sources-2.4.26 But after compiling new kernel and restarting the server , iptables was just plain broken. I had iptables-1.2.8-r1 before , which seems incompatible with kernel 2.4.26. I had to update to the latest version i.e 1.2.11 and then iptables started working. I hope the kernel dependencies are updated to require iptables 1.2.11 or whatever version of iptables is compatible with kernel gentoo-sources-2.4.26.
When upgrading from <2.4.21 to >=2.4.21 iptables needs to be recompiled. I don't think it was said in the 1.2.8 ebuild but rather in the later 1.2.9 ebuilds.