mod_client_state: Throttle stanzas by default

Enable the mod_client_state options "drop_chat_states" and
"queue_presence" by default.  These features are now well-tested in
practice.

ejabberd.yml.example

@@ -577,9 +577,7 @@ modules:
   mod_blocking: {} # requires mod_privacy
   mod_caps: {}
   mod_carboncopy: {}
-  mod_client_state:
-    drop_chat_states: true
-    queue_presence: false
+  mod_client_state: {}
   mod_configure: {} # requires mod_adhoc
   mod_disco: {}
   ## mod_echo: {}

src/mod_client_state.erl

@@ -42,11 +42,11 @@ start(Host, Opts) ->
     QueuePresence = gen_mod:get_opt(queue_presence, Opts,
 				    fun(true) -> true;
 				       (false) -> false
-				    end, false),
+				    end, true),
     DropChatStates = gen_mod:get_opt(drop_chat_states, Opts,
 				     fun(true) -> true;
 				        (false) -> false
-				     end, false),
+				     end, true),
     if QueuePresence; DropChatStates ->
 	   ejabberd_hooks:add(c2s_post_auth_features, Host, ?MODULE,
 			      add_stream_feature, 50),