When using the MS SDK, re-establish LDAP backend connections on a

return code of LDAP_UNAVAILABLE as if it were LDAP_SERVER_DOWN.

With this SDK, LDAP_UNAVAIALBLE is returned when the socket had been closed 
between LDAP API calls.

PR 39095



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@607766 13f79535-47bb-0310-9956-ffa450edef68