void ctl_dns_set_max_ttl(unsigned long ttl);
ctl_dns_set_max_ttl sets the maximum timeout before an entry is deleted from the DNS cache to ttl seconds. The default time to live is 24 hours.
The DNS cache entry for a DNS record is set to the earliest of the time to live set by ctl_dns_set_max_ttl and the time to live returned by the server.
ctl_dns_set_max_ttl is thread-safe.