core: use ethernet::Address from ndn-cxx

refs #2142

Change-Id: I1258a0a1cadbedb31c506c69c84b7906a61fc761
diff --git a/common.hpp b/common.hpp
index b77604e..70943a6 100644
--- a/common.hpp
+++ b/common.hpp
@@ -50,6 +50,7 @@
 #include <ndn-cxx/interest.hpp>
 #include <ndn-cxx/data.hpp>
 #include <ndn-cxx/util/event-emitter.hpp>
+#include <ndn-cxx/util/ethernet.hpp>
 
 #include <boost/algorithm/string.hpp>
 #include <boost/asio.hpp>
@@ -96,6 +97,7 @@
 
 namespace name = ndn::name;
 namespace time = ndn::time;
+namespace ethernet = ndn::util::ethernet;
 
 } // namespace nfd