unbound: fix no-cache feature

[bzfbd]

Years ago I submitted the no-cache feature to unbound which over time broke. I debugged it down to the point that pre-seeding no_cache_store will fix this with minimal changes and make no-cache work again which remains highly valuable in a lot of environments this got deployed.

Obtained from: https://reviews.freebsd.org/D38057

[gthess]

I suspect that this could be broken because of specific module configuration i.e., the module-config: option.
Do you have a specific configuration where this fails?
By default (module-config: 'validator iterator') it works, as there is a testcase for that already.

[bzfbd]

I believe last time I checked was with:
module-config: "dns64 validator iterator