The tree-wide renaming of IUSE="aes-ni" into IUSE="cpu_flags_x86_aes" apparently missed the package net-misc/i2pd, because here the spelling IUSE="aesni" is different. According to the description, the flag here has the meaning of cpu_flags_x86_aes.
Thanks for the report. Fixed the ebuild and added 'aesni' to my search tool. + 02 Feb 2015; Michał Górny <mgorny@gentoo.org> i2pd-0.5.0.ebuild, + i2pd-0.6.0.ebuild, i2pd-9999.ebuild, metadata.xml: + Use cpu_flags_x86_aes, bug #538556.