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>
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 1dface0..dbd64a9 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3263,7 +3263,7 @@
 
 		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);