src: Updating code style to conform (more or less) to ndn-cxx style

Also, adding .clang-format that describes the applied style. Note that
this style requires a slightly customized version of clang-format.
diff --git a/utils/tracers/l2-tracer.cpp b/utils/tracers/l2-tracer.cpp
index 631db7c..bf1fcf1 100644
--- a/utils/tracers/l2-tracer.cpp
+++ b/utils/tracers/l2-tracer.cpp
@@ -32,31 +32,29 @@
 
 namespace ns3 {
 
-L2Tracer::L2Tracer (Ptr<Node> node)
-: m_nodePtr (node)
+L2Tracer::L2Tracer(Ptr<Node> node)
+  : m_nodePtr(node)
 {
-  m_node = boost::lexical_cast<string> (m_nodePtr->GetId ());
+  m_node = boost::lexical_cast<string>(m_nodePtr->GetId());
 
-  Connect ();
+  Connect();
 
-  string name = Names::FindName (node);
-  if (!name.empty ())
-    {
-      m_node = name;
-    }
+  string name = Names::FindName(node);
+  if (!name.empty()) {
+    m_node = name;
+  }
 }
 
 void
-L2Tracer::Connect ()
+L2Tracer::Connect()
 {
-  for (uint32_t devId = 0; devId < m_nodePtr->GetNDevices (); devId ++)
-    {
-      Ptr<PointToPointNetDevice> p2pnd = DynamicCast<PointToPointNetDevice> (m_nodePtr->GetDevice (devId));
-      if (p2pnd)
-        {
-          p2pnd->GetQueue ()->TraceConnectWithoutContext ("Drop", MakeCallback (&L2Tracer::Drop, this));
-        }
+  for (uint32_t devId = 0; devId < m_nodePtr->GetNDevices(); devId++) {
+    Ptr<PointToPointNetDevice> p2pnd =
+      DynamicCast<PointToPointNetDevice>(m_nodePtr->GetDevice(devId));
+    if (p2pnd) {
+      p2pnd->GetQueue()->TraceConnectWithoutContext("Drop", MakeCallback(&L2Tracer::Drop, this));
     }
+  }
 }
 
 } // namespace ns3