cache memory adjustements

cache memory adjustements

The delegation DB now uses the same amount of memory than ADB, which is
1/8 of the `max-cache-size`.

The main cache database, instead of using `max-cache-size`, now use the
"remaining" part of it, after the delegation DB and ADB took their part,
so 6/8.

This avoid blowing up the host memory, typically when specifying
`max-cache-size 95%`, as the global cache usage would go way ahead 100%.