add more diagnostic logs (#8153)

Istio sets listener filter timeout to 10ms by default but requests fail from time to tome. It's very difficult to debug. Even though downstream_pre_cx_timeout_ is exposed to track the number of timeouts, it would be better to have some debug logs.

Description: add more diagnostic logs
Risk Level: low

Signed-off-by: crazyxy <yxyan@google.com>

source/server/connection_handler_impl.cc

@@ -158,7 +158,11 @@ ConnectionHandlerImpl::findActiveListenerByAddress(const Network::Address::Insta
 void ConnectionHandlerImpl::ActiveSocket::onTimeout() {
   listener_.stats_.downstream_pre_cx_timeout_.inc();
   ASSERT(inserted());
+  ENVOY_LOG_TO_LOGGER(listener_.parent_.logger_, debug, "listener filter times out after {} ms",
+                      listener_.listener_filters_timeout_.count());
+
   if (listener_.continue_on_listener_filters_timeout_) {
+    ENVOY_LOG_TO_LOGGER(listener_.parent_.logger_, debug, "fallback to default listener filter");
     newConnection();
   }
   unlink();