Replace hardcoded values in ndn-cxx by MAX_NDN_PACKET_SIZE

Change-Id: I0e116cd2a39781f0d56e156ac517ecadd49b8741
Refs: #3407
diff --git a/src/encoding/encoder.hpp b/src/encoding/encoder.hpp
index a8092d1..540329f 100644
--- a/src/encoding/encoder.hpp
+++ b/src/encoding/encoder.hpp
@@ -42,7 +42,7 @@
    * @param reserveFromBack number of bytes to reserve for append* operations
    */
   explicit
-  Encoder(size_t totalReserve = 8800, size_t reserveFromBack = 400);
+  Encoder(size_t totalReserve = MAX_NDN_PACKET_SIZE, size_t reserveFromBack = 400);
 
   Encoder(const Encoder&) = delete;