Improve externally blocked detection

[DL6ER]

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How familiar are you with the codebase?:

10

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This PR implements two new things:

• Also compare the IPs of queries replied to from cache against the known upstream blacklist IPs. We previously missed these ans displayed them in green as OK (cached) as they are - at first sight - perfectly valid IP addresses in our cache.
• Detect upstream returned NULL address as externally blocked query (Discourse Feature Request)

Test of the two point above:

$ dig c.cx +short
0.0.0.0
$ dig c.cx +short
0.0.0.0

The first query is forwarded to my local unbound (1.8ms) whereas the second is replied to from pi-hole-FTL's cache (1.1ms):

This template was created based on the work of udemy-dl.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/seeing-upstream-null-results-non-changeable/12539/5

[AzureMarker]

Also compare the IPs of queries replied to from cache against the known upstream blacklist IPs. We previously missed these ans displayed them in green as OK (cached) as they are - at first sight - perfectly valid IP addresses in our cache.

Are these changes in this PR?

[DL6ER]

Are these changes in this PR?

My bad, I forgot to git push