lp: add CongestionMark field and tag

refs #3797

Change-Id: I6ac6663c874abde1df2102af81fc03567ad87029
diff --git a/src/detail/face-impl.hpp b/src/detail/face-impl.hpp
index 998ab34..9ce4a69 100644
--- a/src/detail/face-impl.hpp
+++ b/src/detail/face-impl.hpp
@@ -93,6 +93,11 @@
       packet.add<lp::NextHopFaceIdField>(*nextHopFaceIdTag);
     }
 
+    shared_ptr<lp::CongestionMarkTag> congestionMarkTag = interest->getTag<lp::CongestionMarkTag>();
+    if (congestionMarkTag != nullptr) {
+      packet.add<lp::CongestionMarkField>(*congestionMarkTag);
+    }
+
     packet.add<lp::FragmentField>(std::make_pair(interest->wireEncode().begin(),
                                                  interest->wireEncode().end()));