Handle DT_UNKNOWN as DT_REG during file list-up (#13811)

* Handle DT_UNKNOWN as DT_REG during file list-up

Some filesystem does not return dt_type properly. (such as sshfs)
Without this fix, openvino fails to search frontend when mounted on
sshfs.

* style fix

* style fix

src/common/util/src/file_util.cpp

@@ -208,6 +208,10 @@ static void iterate_files_worker(const std::string& path,
                     }
                     break;
                 case DT_REG:
+                case DT_UNKNOWN:
+                    // Comment from READDIR(3):
+                    //     only some filesystems have full support for returning the file type in d_type.
+                    //     All applications must properly handle a return of DT_UNKNOWN.
                     func(path_name, false);
                     break;
                 default: