presence: update delete_subscription documentation

src/modules/presence/doc/presence_admin.xml

@@ -785,8 +785,8 @@ modparam("presence", "subs_remove_match", 1)
 			give extra control of deleting the subscription after processing of
 			event_route[presence:notify-reply]. If value = 1, it deletes the subscription.
 			If xavp_cfg parameter is set but this attribute is not in the avp,
-			the subscription is not deleted. this does apply for code 404 and 481
-			where subscription is deleted.</para>
+			the subscription is not deleted. this does not apply for codes 404, 481
+			and 408 (when timeout_rm_subs = 1) where subscription is deleted.</para>
         </listitem>
      </itemizedlist>
     <para>