Remove use of deprecated and now removed QueueBase::MaxPackets

Change-Id: I6aa6d2af4e6189ecd6bac774b2b846b18a0f9dd2
diff --git a/tests/unit-tests/helper/ndn-stack-helper.t.cpp b/tests/unit-tests/helper/ndn-stack-helper.t.cpp
index 04d5bba..2fc98b6 100644
--- a/tests/unit-tests/helper/ndn-stack-helper.t.cpp
+++ b/tests/unit-tests/helper/ndn-stack-helper.t.cpp
@@ -32,7 +32,7 @@
   // setting default parameters for PointToPoint links and channels
   Config::SetDefault("ns3::PointToPointNetDevice::DataRate", StringValue("10Mbps"));
   Config::SetDefault("ns3::PointToPointChannel::Delay", StringValue("10ms"));
-  Config::SetDefault("ns3::QueueBase::MaxPackets", UintegerValue(20));
+  Config::SetDefault("ns3::QueueBase::MaxSize", StringValue("20p"));
 
   // Creating nodes
   NodeContainer nodes;