nfsd: clean up an xdr reserved space calculation

We should use XDR_LEN to calculate reserved space in case the oid is not
a multiple of 4.

RESERVE_SPACE actually rounds up for us, but it's probably better to be
careful here.
Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4xdr.c

@@ -3263,7 +3263,7 @@ nfsd4_do_encode_secinfo(struct nfsd4_compoundres *resp,
 
 		if (rpcauth_get_gssinfo(pf, &info) == 0) {
 			supported++;
-			RESERVE_SPACE(4 + 4 + info.oid.len + 4 + 4);
+			RESERVE_SPACE(4 + 4 + XDR_LEN(info.oid.len) + 4 + 4);
 			WRITE32(RPC_AUTH_GSS);
 			WRITE32(info.oid.len);
 			WRITEMEM(info.oid.data, info.oid.len);