Here is a fix for the bug that doesn't need a kernel patch.

To re-instate the old behaviour - ticket expiry returns EACCESS - just
apply this patch and run rpc.gssd with the "-e" option (add
RPCGSSDOPTS=-e to /etc/default/nfs-common).


The patch has been sent upstream, I'm just adding to the bug report in
case anyone wants to try it out