CVE-2026-31644: net: lan966x: fix use-after-free and leak in lan966x_fdma_reload()

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

net: lan966x: fix use-after-free and leak in lan966xfdmareload()

When lan966xfdmareload() fails to allocate new RX buffers, the restore path restarts DMA using old descriptors whose pages were already freed via lan966xfdmarxfreepages(). Since pagepoolputfullpage() can release pages back to the buddy allocator, the hardware may DMA into memory now owned by other kernel subsystems.

Additionally, on the restore path, the newly created page pool (if allocation partially succeeded) is overwritten without being destroyed, leaking it.

Fix both issues by deferring the release of old pages until after the new allocation succeeds. Save the old page array before the allocation so old pages can be freed on the success path. On the failure path, the old descriptors, pages and page pool are all still valid, making the restore safe. Also ensure the restore path re-enables NAPI and wakes the netdev, matching the success path.