encoding+lp: declare constexpr and noexcept where possible

Change-Id: Icf708af0b77d62d7d8e75527aaf51c7178e47125
diff --git a/tests/unit-tests/encoding/tlv.t.cpp b/tests/unit-tests/encoding/tlv.t.cpp
index 299b31c..f8e2f9e 100644
--- a/tests/unit-tests/encoding/tlv.t.cpp
+++ b/tests/unit-tests/encoding/tlv.t.cpp
@@ -20,6 +20,7 @@
  */
 
 #include "encoding/tlv.hpp"
+#include "encoding/buffer.hpp"
 
 #include "boost-test.hpp"