daemon: Reload face_system section of the config file when NIC configuration changes

The main desired effect of the reloading is re-creation of multicast
faces, e.g., when a new interface appears in the system.

Change-Id: I8384e5f96285ddca363981c92e1b6de39e0072ef
Refs: #2460
diff --git a/daemon/nfd.hpp b/daemon/nfd.hpp
index 92e6efd..4710554 100644
--- a/daemon/nfd.hpp
+++ b/daemon/nfd.hpp
@@ -28,8 +28,10 @@
 
 #include "common.hpp"
 #include "core/config-file.hpp"
+#include "core/scheduler.hpp"
 
 #include <ndn-cxx/security/key-chain.hpp>
+#include <ndn-cxx/util/network-monitor.hpp>
 
 namespace nfd {
 
@@ -86,6 +88,9 @@
   void
   initializeManagement();
 
+  void
+  reloadConfigFileFaceSection();
+
 private:
   std::string m_configFile;
   ConfigSection m_configSection;
@@ -99,6 +104,9 @@
   unique_ptr<StatusServer>          m_statusServer;
 
   ndn::KeyChain&                    m_keyChain;
+
+  ndn::util::NetworkMonitor         m_networkMonitor;
+  scheduler::ScopedEventId          m_reloadConfigEvent;
 };
 
 } // namespace nfd