Title: #806: sudo: always use server highest usn for smart refresh
I'm not sure what do you mean. From what I read in the code I see
1. `srv_opts->last_usn` is updated by reading `lastUSN` attribute from `rootDSE`
when new connection is established (sdap id op code or online check code)
It is unfortunately not updated if the old and the new server are the same (see my patch
above). And since we try to stick to one server this will happen most of the time.
2. It gets also updated when enumerating users/groups/services and sudo smart refresh
if any object found by the enumeration have `entryUSN` > `srv_opts->last_usn`.
yes, but typically we do not recommend to enable enumeration, so you cannot rely on it.
So it does not necessarily corresponds to real value of `lastUSN` attribute but it
contains greatest USN value known to SSSD.
See the full comment at https://github.com/SSSD/sssd/pull/806#issuecomment-489603482