Replace hardcoded values in ndn-cxx by MAX_NDN_PACKET_SIZE

Change-Id: I0e116cd2a39781f0d56e156ac517ecadd49b8741
Refs: #3407
diff --git a/src/encoding/encoding-buffer.hpp b/src/encoding/encoding-buffer.hpp
index 67cc4bb..9ab9239 100644
--- a/src/encoding/encoding-buffer.hpp
+++ b/src/encoding/encoding-buffer.hpp
@@ -38,7 +38,7 @@
 {
 public:
   explicit
-  EncodingImpl(size_t totalReserve = 8800, size_t reserveFromBack = 400)
+  EncodingImpl(size_t totalReserve = MAX_NDN_PACKET_SIZE, size_t reserveFromBack = 400)
     : Encoder(totalReserve, reserveFromBack)
   {
   }