Call Session::loop with send_closure_later to unify stack traces.

td/telegram/net/Session.cpp

@@ -1511,6 +1511,10 @@ void Session::auth_loop(double now) {
   }
 }
 
+void Session::timeout_expired() {
+  send_closure_later(actor_id(this), &Session::loop);
+}
+
 void Session::loop() {
   if (!was_on_network_) {
     return;

td/telegram/net/Session.h

@@ -265,6 +265,7 @@ class Session final
   void on_check_key_result(NetQueryPtr query);
 
   void start_up() final;
+  void timeout_expired() final;
   void loop() final;
   void hangup() final;
   void raw_event(const Event::Raw &event) final;