Bug 644608 - RHDS 8.1->8.2 upgrade fails to properly migrate ACIs

https://bugzilla.redhat.com/show_bug.cgi?id=644608

Description:
Previous cherry-pick commit 5cd9fc9826fd88b8672129e41523065c0b692c3b
failed the merge for setting a special dup compare callback
ai_dup_cmp_fn when it is set.

ldap/servers/slapd/back-ldbm/dblayer.c

@@ -2812,7 +2812,12 @@ _dblayer_set_db_callbacks(dblayer_private *priv, DB *dbp, struct attrinfo *ai)
         if (rc)
             return rc;
 
-        rc = dbp->set_dup_compare( dbp, idl_new_compare_dups);
+        if (ai->ai_dup_cmp_fn) {
+            /* If set, use the special dup compare callback */
+            rc = dbp->set_dup_compare(dbp, ai->ai_dup_cmp_fn);
+        } else {
+            rc = dbp->set_dup_compare(dbp, idl_new_compare_dups);
+        }
         if (rc)
             return rc;
     }