rec: Don't retry security polling too often when it fails

[rgacogne]

Short description

Even if the security polling fails because of a Servfail or DNSSEC validation, there is no reason to retry right away during the next houseKeeping() iteration. On recursor with an important workload, we could end up doing a security polling every second.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled and tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)