Update the database query counting the number of banned IPs to filter out
any bans that have already expired. An expired ban is defined as a ban
where the "time of ban" plus the "duration of ban" is less than the
current time.
This is necessary because bans that have expired are not automatically
removed from the database and will cause metrics to diverge from the counts
reported by `fail2ban-client`.
526b1c7272