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 <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>
Reviewed-by: Benjamin Coddington <[e-mail]>
Signed-off-by: Anna Schumaker <[e-mail]>

fs/nfs/callback_proc.c

···
 
 	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();