dns/opendnssec2: upgrade 2.1.4 -> 2.1.6

This release of 2.1.6 fixes some issues regarding the key list
wrongfully displayed (a regression bug in 2.1.5) as well as a small
leak in the enforcer (which can add up when you bang the enforcer
with a lot of commands. And as well as a serious signing error when
using Combined Signing Keys (CSKs), this is only relevant if you
combine KSK and ZSK in one. Especially users of CSKs need this fix
now. Another nice fix is a reconnect to a MySQL/MariaDB database
you you don't have to tweak database parameters.

PR: 244047
Submitted by: Jaap Akkerhuis <jaap@NLnetLabs.nl> (maintainer)
Relnotes: https://www.opendnssec.org/2019/11/opendnssec-2-1-5/

		https://www.opendnssec.org/2020/02/opendnssec-2-1-6/