PR 229939 (https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=229939) documents a problem whereby a server is serving LDAP and kdc, the kdc starts before slapd. This patch ensures slapd starts before kdc.
The reason to patch openldap24-server is etc/rc.d/kdc in base cannot depend on a port starting. Another option might be to provide a kdc startup script in ports/security/krb5-*, however users may still use the base provided kdc script, therefore this is probably the best option.