mod_ldap: add TRACE5 for LDAP retries

trunk patch: http://svn.apache.org/r1510085

Submitted by: covener
Reviewed by: jim, humbedooh


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1523266 13f79535-47bb-0310-9956-ffa450edef68