build: Fix compilation due to refactoring of EncodingImpl in ndn-cxx library

Change-Id: Ibab900083b6c82b94e2b018c9134b366fcaef523
Refs: #2494
diff --git a/src/state.cpp b/src/state.cpp
index 251d46b..7b1877b 100644
--- a/src/state.cpp
+++ b/src/state.cpp
@@ -104,7 +104,7 @@
   BOOST_REVERSE_FOREACH (ConstLeafPtr leaf, m_leaves.get<ordered>())
     {
       size_t entryLength = 0;
-      entryLength += prependNonNegativeIntegerBlock(block, tlv::SeqNo, leaf->getSeq());
+      entryLength += ndn::prependNonNegativeIntegerBlock(block, tlv::SeqNo, leaf->getSeq());
       entryLength += leaf->getSessionName().wireEncode(block);
       entryLength += block.prependVarNumber(entryLength);
       entryLength += block.prependVarNumber(tlv::StateLeaf);