Have a look here, it explains LDAP settings and should work for your QNAP too:
LDAP server host: your nethserver
Base DN: dc=directory,dc=nh
Root DN: cn=ldapservice,dc=directory,dc=nh
Users base DN: ou=People,dc=directory,dc=nh
Group base DN: ou=Groups,dc=directory,dc=nh
See account-provider-test dump on your Nethserver for more infos.