CVE-2026-74634: ring-buffer: Prevent subbuf order change when resizing is disabled

In the Linux kernel, the following vulnerability has been resolved:

ring-buffer: Prevent subbuf order change when resizing is disabled

Because ringbuffersubbuforderset() frees buffer pages, we can't allow it when resizing is disabled. A non-consuming reader is at risk of use-after-free (rbadvanceiter()).

Return -EBUSY on resizedisabled, matching ringbufferresize() behaviour.