Use `inline` on all namespace-scope constants defined in headers

Change-Id: Ic61f8d26f59fdc2895415ca47065c02d6eec28ed
diff --git a/daemon/face/lp-fragmenter.cpp b/daemon/face/lp-fragmenter.cpp
index 0243a48..a9fcf17 100644
--- a/daemon/face/lp-fragmenter.cpp
+++ b/daemon/face/lp-fragmenter.cpp
@@ -41,7 +41,7 @@
 /**
  * \brief Maximum overhead on a single fragment, not counting other NDNLPv2 headers.
  */
-const size_t MAX_SINGLE_FRAG_OVERHEAD =
+constexpr size_t MAX_SINGLE_FRAG_OVERHEAD =
   1 + 9 + // LpPacket TLV-TYPE and TLV-LENGTH
   1 + 1 + 8 + // Sequence TLV
   1 + 9; // Fragment TLV-TYPE and TLV-LENGTH
@@ -49,7 +49,7 @@
 /**
  * \brief Maximum overhead of adding fragmentation to payload, not counting other NDNLPv2 headers.
  */
-const size_t MAX_FRAG_OVERHEAD =
+constexpr size_t MAX_FRAG_OVERHEAD =
   1 + 9 + // LpPacket TLV-TYPE and TLV-LENGTH
   1 + 1 + 8 + // Sequence TLV
   1 + 1 + 8 + // FragIndex TLV