Actually implement set_network_delay

Change-Id: I11de092c21a9b6d449448e84935da52ae3fbe93c
diff --git a/aos/events/simulated_event_loop.h b/aos/events/simulated_event_loop.h
index a7f7920..7718cfb 100644
--- a/aos/events/simulated_event_loop.h
+++ b/aos/events/simulated_event_loop.h
@@ -87,7 +87,9 @@
   std::chrono::nanoseconds send_delay() const { return send_delay_; }
 
   // Sets the simulated network delay for messages forwarded between nodes.
-  void set_network_delay(std::chrono::nanoseconds network_delay);
+  void set_network_delay(std::chrono::nanoseconds network_delay) {
+    network_delay_ = network_delay;
+  }
   std::chrono::nanoseconds network_delay() const { return network_delay_; }
 
   // Returns the clock used to synchronize the nodes.