Don't cache hosts as services

Don't cache hosts as services

This was kind of abuse of struct cache_service and the tree storing all
cached entries. Host isn't really a service, treating it so required
extra checks whenever dealing with cached entries.

Now we converted all code to read DNS records A and AAAA directly we
don't need to store these faked services.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>