net/kea-devel: Repocopy from net/kea

The 2.6.x branch of kea has a number of limitations that require it
be patched for the boost upgrade. We will import the 2.7.x (development)
branch of kea as kea-devel.

Note that just like bind9, also developed by ISC (isc.org), even version
numbers, i.e. 2.6, are stable branch while odd numbered version numbers,
i.e. 2.7, are development branch.