Add OpenIKED, version 1.0

This is OpenBSD's OpenIKED with fixes and improvements and additional
features.

Original author: Reyk Floeter <reyk@openbsd.org>
Author: Marcel Moolenaar <marcel@brkt.com>
Reviewed by: mat@
Approved by: mat@
Obtained from: https://github.com/xcllnt/openiked
Sponsored by: Bracket Computing, Inc.
Differential Revision: https://reviews.freebsd.org/D8417