CVE-2026-74316: NFSD: Handle layout stid in nfsd4_drop_revoked_stid()

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

NFSD: Handle layout stid in nfsd4droprevokedstid()

nfsd4droprevokedstid() has no SCTYPELAYOUT case, so when a client sends FREESTATEID for an admin-revoked layout stid, the default branch releases cllock and returns without unhashing or releasing the stid. The stid remains in the IDR and on the per-client list until the client is destroyed.

Remove the layout stid from the per-client list and call nfs4putstid() to drop the creation reference. When the refcount reaches zero, nfsd4freelayoutstateid() handles the remaining cleanup: cancelling the fence worker, removing from the per-file list, and freeing the slab object.