config: check for available databases

We need to have: GEOIP_CITY_EDITION_REV1, GEOIP_CITY_EDITION_REV1_V6,
GEOIP_COUNTRY_EDITION, GEOIP_COUNTRY_EDITION_V6, GEOIP_ASNUM_EDITION,
GEOIP_ASNUM_EDITION_V6. Not all might be available on older versions.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>