[ndnSIM] Correct encoding of HopCount

Properly use NonNegativeInteger encoding instead of previously used
fixed-length 8-byte encoding of uint64_t
diff --git a/ndn-cxx/lp/fields.hpp b/ndn-cxx/lp/fields.hpp
index fbe5305..8241b7a 100644
--- a/ndn-cxx/lp/fields.hpp
+++ b/ndn-cxx/lp/fields.hpp
@@ -111,8 +111,11 @@
 BOOST_CONCEPT_ASSERT((Field<PrefixAnnouncementField>));
 
 typedef FieldDecl<field_location_tags::Header,
-                  uint64_t,
-                  tlv::HopCountTag> HopCountTagField;
+                  uint16_t,
+                  tlv::HopCountTag,
+                  false,
+                  NonNegativeIntegerTag,
+                  NonNegativeIntegerTag> HopCountTagField;
 BOOST_CONCEPT_ASSERT((Field<HopCountTagField>));
 
 typedef FieldDecl<field_location_tags::Header,