publisher: fix encoding bug in routing table publisher

refs: #4453

Change-Id: I03e819e963f0957f3d40ff25e378f2b9b17357b7
diff --git a/src/tlv/nexthop.hpp b/src/tlv/nexthop.hpp
index 03666cc..9b0f72c 100644
--- a/src/tlv/nexthop.hpp
+++ b/src/tlv/nexthop.hpp
@@ -103,6 +103,8 @@
   mutable ndn::Block m_wire;
 };
 
+NDN_CXX_DECLARE_WIRE_ENCODE_INSTANTIATIONS(NextHop);
+
 std::ostream&
 operator<<(std::ostream& os, const NextHop& nexthop);