security/munge: Update to 0.5.16

Packaged in wip by J Bacon

The next paragraph describes the pkgsrc-specific packaging changes,
if any.

The next paragraph summarizes the upstream changes on a high level.
In packages following the GNU Coding Standards, these changes are in
the NEWS file, see
https://www.gnu.org/prep/standards/html_node/NEWS-File.html.

See https://www.pkgsrc.org/wip/users/#COMMIT_MSG.