face: use /run/nfd.sock on Linux

refs #5039

Change-Id: I10902725912a8f194ce6da6590378c1029955f80
diff --git a/daemon/rib/service.cpp b/daemon/rib/service.cpp
index d9e5bc5..596fa27 100644
--- a/daemon/rib/service.cpp
+++ b/daemon/rib/service.cpp
@@ -73,7 +73,11 @@
 {
   if (config.get_child_optional("face_system.unix")) {
     // default socket path should be the same as in UnixStreamFactory::processConfig
+#ifdef __linux__
+    auto path = config.get<std::string>("face_system.unix.path", "/run/nfd.sock");
+#else
     auto path = config.get<std::string>("face_system.unix.path", "/var/run/nfd.sock");
+#endif // __linux__
     return make_shared<ndn::UnixTransport>(path);
   }
   else if (config.get_child_optional("face_system.tcp") &&