Adjust TTL for MANTIS adapter

[parisholley]

Existing adapter has incorrect TTL of 24 hours hard coded, change will allow for TTL overriding by server response at bid or global level

[bretg]

Looks good - thanks. A smaller default TTL might still be desirable, but assuming your responses normally contain TTLs in the order of minutes rather than hours, the net effect is what we're looking for.