Most of the settings (durations) are already inheriting from the default
because they use the constants from lib/dns/kasp.h. We need them as
constants so we can use them in named-checkconf to verify the policy
parameters.
The NSEC(3) parameters and keys should come from the actual default
policy. Change the call to cfg_kasp_fromconfig() to include the default
kasp. We also no longer need to corner case where config is NULL we load
the built-in policy: the built-in policies are now loaded when config is
set to named_g_config.
Finally, add a debug log (it is useful to see which policies are being
loaded).
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