CSMA Cleanup, XXX in echo apps, clarification of point-to-point data rates in dox

tutorial/tutorial-csma-echo-ascii-trace.cc

@@ -38,7 +38,7 @@ main (int argc, char *argv[])
   internet.Install (n);
 
   CsmaHelper csma;
-  csma.SetChannelParameter ("BitRate", StringValue ("5Mpbs"));
+  csma.SetChannelParameter ("DataRate", StringValue ("5Mpbs"));
   csma.SetChannelParameter ("Delay", StringValue ("2ms"));
   NetDeviceContainer nd = csma.Install (n);