openldap: version update and new build parameters

openldap: version update and new build parameters

This patch updates OpenLDAP to 2.4.47, introduces new build
parameters and places openldap-server, openldap-utils and
libopenldap under a separate menu item in Network.

OpenLDAP is difficult to find in menuconfig at present. Making
a separate menu item for OpenLDAP for selection of packages and
enabling or disabling build parameters makes better sense.

To have access to the loglevel directive, OpenLDAP must be built
with debugging information. Having access to the loglevel directive
is essential during the initial configuration of OpenLDAP server.

International users may want to enable ICU support to have access
to international characters.

Signed-off-by: Val Kulkov <val.kulkov@gmail.com>