nfsd: Fix bad reserving space for encoding rdattr_error

Introduced by commit 561f0ed4 (nfsd4: allow large readdirs).
Signed-off-by: NKinglong Mee <kinglongmee@gmail.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -2641,7 +2641,7 @@ nfsd4_encode_rdattr_error(struct xdr_stream *xdr, __be32 nfserr)
 {
 	__be32 *p;
 
-	p = xdr_reserve_space(xdr, 6);
+	p = xdr_reserve_space(xdr, 20);
 	if (!p)
 		return NULL;
 	*p++ = htonl(2);