Ever since e5099643edcd981586507f486a885fd797cd7be3 mtr is no longer installed with cap_net_raw on usr/sbin/mtr because pkg_postinst is overwritten without calling fcaps_pkg_postinst. From https://devmanual.gentoo.org/eclass-reference/fcaps.eclass/index.html: Note: If you override pkg_postinst, you must call fcaps_pkg_postinst yourself.
Thanks, I missed that one. Fixed now!