move test code to anon namespace

src/common/packet-metadata-test.cc

@@ -28,7 +28,9 @@
 #include "packet.h"
 #include "packet-metadata.h"
 
-namespace ns3 {
+using namespace ns3;
+
+namespace {
 
 template <int N>
 class HistoryHeader : public Header
@@ -191,6 +193,10 @@ HistoryTrailer<N>::Deserialize (Buffer::Iterator start)
   return N;
 }
 
+}
+
+namespace ns3 {
+
 
 
 class PacketMetadataTest : public Test {