dnsdist-1.8.x: Automatically load Lua FFI inspection functions

[rgacogne]

Short description

Backport of #12923 to rel/dnsdist-1.8.x.

We used to do that for all Lua FFI functions except the ones used for inspecting StatNode objects.

(cherry picked from commit b4fbe20)

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master