Change default database path and configuration directory

Now respectively ${LOCALSTATEDIR}/lib/ndn/ndns/ndns.db
and ${SYSCONFDIR}/ndn/ndns

Refs: #4810
Change-Id: I351a6a15f8daa0a032845cb26d5d76179faa7b27
diff --git a/src/daemon/db-mgr.hpp b/src/daemon/db-mgr.hpp
index c21b3e0..a41380a 100644
--- a/src/daemon/db-mgr.hpp
+++ b/src/daemon/db-mgr.hpp
@@ -65,7 +65,7 @@
 
 public:
   explicit
-  DbMgr(const std::string& dbFile = DEFAULT_DATABASE_PATH "/" "ndns.db");
+  DbMgr(const std::string& dbFile = "");
 
   ~DbMgr();