encoding: add ad hoc link type to ndn::nfd::LinkType enum

refs: #3967

Change-Id: I443d3e43dc31dec2e2426c61b7a92d480871f34a
diff --git a/src/encoding/nfd-constants.cpp b/src/encoding/nfd-constants.cpp
index b502a9c..9cda265 100644
--- a/src/encoding/nfd-constants.cpp
+++ b/src/encoding/nfd-constants.cpp
@@ -68,6 +68,8 @@
       return os << "point-to-point";
     case LINK_TYPE_MULTI_ACCESS:
       return os << "multi-access";
+    case LINK_TYPE_AD_HOC:
+      return os << "adhoc";
   }
   return os << static_cast<unsigned>(linkType);
 }