[(no branch, rebasing pemensik/dhcp-ldap-gssapi-principal)] Do not report missed...

[(no branch, rebasing pemensik/dhcp-ldap-gssapi-principal)] Do not report missed ldap-gssapi-pricipal as error

If DHCP is built with ldap_gssapi support but ldap-gssapi-principal
is not set error level messages is written in the logs.  This is
totally OK to not have the parameter set. Report names of required
options, not internal code variables.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1831332

Signed-off-by: Pavel Zhukov <pzhukov@redhat.com>
Signed-off-by: Petr Menšík <pemensik@redhat.com>