mgmt: fix compilation error on Xcode 8 and earlier

refs #4639

Change-Id: I3c2af9e60f3a9c0c959bd6a52d65c308c234efac
diff --git a/src/mgmt/nfd/controller.hpp b/src/mgmt/nfd/controller.hpp
index aeb4692..e98b606 100644
--- a/src/mgmt/nfd/controller.hpp
+++ b/src/mgmt/nfd/controller.hpp
@@ -74,7 +74,7 @@
   start(const ControlParameters& parameters,
         const CommandSucceedCallback& onSuccess,
         const CommandFailCallback& onFailure,
-        const CommandOptions& options = {})
+        const CommandOptions& options = CommandOptions())
   {
     shared_ptr<ControlCommand> command = make_shared<Command>();
     this->startCommand(command, parameters, onSuccess, onFailure, options);
@@ -86,7 +86,7 @@
   std::enable_if_t<std::is_default_constructible<Dataset>::value>
   fetch(const std::function<void(typename Dataset::ResultType)>& onSuccess,
         const DatasetFailCallback& onFailure,
-        const CommandOptions& options = {})
+        const CommandOptions& options = CommandOptions())
   {
     this->fetchDataset(make_shared<Dataset>(), onSuccess, onFailure, options);
   }
@@ -98,7 +98,7 @@
   fetch(const ParamType& param,
         const std::function<void(typename Dataset::ResultType)>& onSuccess,
         const DatasetFailCallback& onFailure,
-        const CommandOptions& options = {})
+        const CommandOptions& options = CommandOptions())
   {
     this->fetchDataset(make_shared<Dataset>(param), onSuccess, onFailure, options);
   }