tests: Fixing occasional failure of the ndn-net-device unit test

Change-Id: I471023fc23ffaebe04d9668426b4c1b03e4974ae
Refs: #3059
diff --git a/tests/unit-tests/model/ndn-net-device-face.t.cpp b/tests/unit-tests/model/ndn-net-device-face.t.cpp
index 23a6406..1c886aa 100644
--- a/tests/unit-tests/model/ndn-net-device-face.t.cpp
+++ b/tests/unit-tests/model/ndn-net-device-face.t.cpp
@@ -73,11 +73,12 @@
 
   auto node1_netDeviceFace = std::dynamic_pointer_cast<NetDeviceFace>(node0_faceContainer->Get(node1Face_iterator));
 
-  Simulator::Stop(Seconds(20.0));
+  Simulator::Stop(Seconds(20.001));
   Simulator::Run();
 
   ::ndn::nfd::FaceStatus faceStatus = node1_netDeviceFace->getFaceStatus();
   BOOST_CHECK_EQUAL(faceStatus.getNInInterests(), 2000);
+
   Simulator::Destroy();
 }