path-util: fix fstat fallback in fd_is_mount_point

src/shared/path-util.c

@@ -512,7 +512,7 @@ static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id
 int fd_is_mount_point(int fd) {
         union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;
         int mount_id = -1, mount_id_parent = -1;
-        bool nosupp = false, check_st_dev = false;
+        bool nosupp = false, check_st_dev = true;
         struct stat a, b;
         int r;