dispatcher: docs - added modparams for keepalives in sample config file

src/modules/dispatcher/doc/dispatcher.cfg

@@ -121,6 +121,10 @@ modparam("dispatcher", "table_name", "dispatcher")
 modparam("dispatcher", "flags", 2)
 modparam("dispatcher", "xavp_dst", "_dsdst_")
 modparam("dispatcher", "xavp_ctx", "_dsctx_")
+modparam("dispatcher", "ds_ping_from", "sip:[email protected]")
+modparam("dispatcher", "ds_ping_interval", 60)
+modparam("dispatcher", "ds_probing_mode", 1)
+modparam("dispatcher", "ds_timer_mode", 1)
 
 ####### Routing Logic ########