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);
 }
diff --git a/src/encoding/nfd-constants.hpp b/src/encoding/nfd-constants.hpp
index 8b57def..de19776 100644
--- a/src/encoding/nfd-constants.hpp
+++ b/src/encoding/nfd-constants.hpp
@@ -58,6 +58,7 @@
   LINK_TYPE_NONE           = std::numeric_limits<uint8_t>::max(),
   LINK_TYPE_POINT_TO_POINT = 0, ///< link is point-to-point
   LINK_TYPE_MULTI_ACCESS   = 1, ///< link is multi-access
+  LINK_TYPE_AD_HOC         = 2, ///< link is ad hoc
 };
 
 std::ostream&