By default, we enabled flattening of the network tree when we export it.

However, this is only required for xt_geoip since the other formats can
deal with overlapping networks and would even benefit from a shorter
list.

Therefore this is now only enabled when needed which results in shorter
export times (9 seconds instead of 2.5 minutes) and the full ipset is
about 20% smaller when loaded into memory than before.
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>