OpenSSL throws warnings left and right otherwise.  LibreSSL don't
care, but let's just keep this for now, not sure what this might
break otherwise.

Submitted by: Nasantogtokh Amarsaikhan <minerva2991 AT gmail DOT com>

(legacy) use reverse mask instead of reverse address for ddns in dhcpd (https://github.com/opnsense/core/issues/352)

Crash report would pop up twice, that is confusing.