Debian has a patch for this: https://packages.debian.org/source/unstable/libapache2-mod-rpaf
+*mod_rpaf-0.6-r1 (09 May 2015) + + 09 May 2015; Pacho Ramos <pacho@gentoo.org> +files/003_ipv6.patch, + +files/010_multiple_proxies.patch, +files/011_apache2.4.patch, + +files/012_Add-missing-header-for-inet_addr.patch, +mod_rpaf-0.6-r1.ebuild: + Apply debian patches also adding support for apache 2.4 (#532864) +