minor: add active mode documentation to the template service.properties

SVN: 21480

datastore_server/dist/etc/service.properties

@@ -362,9 +362,17 @@ dss-rpc.put-default = main-thread
 # way to interact with their data (i.e. via an FTP client).  
 #ftp.server.enable=false
 #
-# port where the FTP server will be started. Optional parameter, default value is 2121
+# port where the FTP event connections will be opened. Optional parameter, default value is 2121.
 #ftp.server.port=2121
 #
+# when set to true enables the FTP server to run in "active mode". This means data connections
+# will always go to a single pre-configured port on the server. Such a configuration can ease the 
+# server firewall administration (only one additional port should be opened).
+#ftp.server.activemode.enable=true
+#
+# the active mode port number configuration. Default value is 2122.
+#ftp.server.activemode.port=2122
+#
 # Similar to the global 'use-ssl' parameter. When set to 'true' all 'keystore' properties become mandatory.
 #ftp.server.use-ssl=true
 #