Remove use of deprecated and now removed QueueBase::MaxPackets

Change-Id: I6aa6d2af4e6189ecd6bac774b2b846b18a0f9dd2
diff --git a/examples/ndn-csma.cpp b/examples/ndn-csma.cpp
index a30b0e5..5e0ccfd 100644
--- a/examples/ndn-csma.cpp
+++ b/examples/ndn-csma.cpp
@@ -55,7 +55,7 @@
   // setting default parameters for PointToPoint links and channels
   Config::SetDefault("ns3::CsmaChannel::DataRate", StringValue("1Mbps"));
   Config::SetDefault("ns3::CsmaChannel::Delay", StringValue("10ms"));
-  Config::SetDefault("ns3::QueueBase::MaxPackets", UintegerValue(20));
+  Config::SetDefault("ns3::QueueBase::MaxSize", StringValue("20p"));
 
   // Read optional command-line parameters (e.g., enable visualizer with ./waf --run=<> --visualize
   CommandLine cmd;