Allow larger TTL values in zones that go insecure. This is necessary
because otherwise the zone will not be loaded due to the max-zone-ttl
of P1D that is part of the current insecure policy.
In the keymgr.c code, default back to P1D if the max-zone-ttl is set
to zero.
(cherry picked from commit dc6dafdad1)
a21407d062