mount-util: beef up bind_remount_recursive() to be able to toggle more than MS_RDONLY

The function is otherwise generic enough to toggle other bind mount
flags beyond MS_RDONLY (for example: MS_NOSUID or MS_NODEV), hence let's
beef it up slightly to support that too.

src/volatile-root/volatile-root.c

@@ -42,7 +42,7 @@ static int make_volatile(const char *path) {
         if (r < 0)
                 goto finish_umount;
 
-        r = bind_remount_recursive("/run/systemd/volatile-sysroot/usr", true, NULL);
+        r = bind_remount_recursive("/run/systemd/volatile-sysroot/usr", MS_RDONLY, MS_RDONLY, NULL);
         if (r < 0) {
                 log_error_errno(r, "Failed to remount /usr read-only: %m");
                 goto finish_umount;