sudo: add a threshold option to reduce size of rules refresh filter
If a large number of rules is expired at one time the ldap filter may
become too large to be processed by server. This commits adds a new
option "sudo_threshold" to sudo responder. If the threshold is
exceeded a full refreshed is done instead of rules refresh.
Reviewed-by: Jakub Hrozek <firstname.lastname@example.org>
Reviewed-by: Fabiano Fidêncio <email@example.com>