export: Flatten the tree before exporting it

export: Flatten the tree before exporting it

This patch removes the possibility that any IP address ranges
might show up in multiple exported files.

If this was content from the database:

  * 10.0.0.0/16 - DE
  * 10.0.1.0/24 - FR

Then the IP address 10.0.1.1 would match for both countries.

The algorithm will now break the larger /16 subnet apart into
smaller subnets so that 10.0.1.0/24 is no longer overlapped.

There was some time spent on this to make this as efficient
as possible.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>