nfsd: fix nfsd4_encode_open buffer space reservation

nfsd4_encode_open first reservation is currently for 36 + sizeof(stateid_t)
while it writes after the stateid a cinfo (20 bytes) and 5 more 4-bytes
words, for a total of 40 + sizeof(stateid_t).
Signed-off-by: NBenny Halevy <bhalevy@panasas.com>
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4xdr.c

@@ -2133,7 +2133,7 @@ nfsd4_encode_open(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_op
 	if (nfserr)
 		goto out;
 
-	RESERVE_SPACE(36 + sizeof(stateid_t));
+	RESERVE_SPACE(40 + sizeof(stateid_t));
 	WRITE32(open->op_stateid.si_generation);
 	WRITEMEM(&open->op_stateid.si_opaque, sizeof(stateid_opaque_t));
 	WRITECINFO(open->op_cinfo);