Log server map send cycle time. (#13259)

* Measure server map send time per player.

src/clientiface.h

@@ -423,6 +423,9 @@ private:
 	// CPU usage optimization
 	float m_nothing_to_send_pause_timer = 0.0f;
 
+	// measure how long it takes the server to send the complete map
+	float m_map_send_completion_timer = 0.0f;
+
 	/*
 		name of player using this client
 	*/