NFS: CB_OFFLOAD can return NFS4ERR_DELAY

RFC 7862 permits the callback service to respond to a CB_OFFLOAD
operation with NFS4ERR_DELAY. Use that instead of
NFS4ERR_SERVERFAULT for temporary memory allocation failure, as that
is more consistent with how other operations report memory
allocation failure.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

fs/nfs/callback_proc.c

@@ -718,7 +718,7 @@ __be32 nfs4_callback_offload(void *data, void *dummy,
 
 	copy = kzalloc(sizeof(struct nfs4_copy_state), GFP_KERNEL);
 	if (!copy)
-		return htonl(NFS4ERR_SERVERFAULT);
+		return cpu_to_be32(NFS4ERR_DELAY);
 
 	spin_lock(&cps->clp->cl_lock);
 	rcu_read_lock();