CORE-14326: Work around limitation using LENGTH_UNLIMITED string (#671)

Author: alexcamposruiz

examples/connext_dds/flat_data_latency/c++11/USER_QOS_PROFILES.xml

@@ -34,7 +34,7 @@
                     <value>
                         <element>
                             <name>dds.data_writer.history.memory_manager.fast_pool.pool_buffer_max_size</name>
-                            <value>LENGTH_UNLIMITED</value>
+                            <value>-1</value> <!-- unlimited -->
                         </element>
                     </value>
                 </property>