Add smart_ip support as additional alternative to detect a country (for IPv6 support)

Hello.

This beautiful module can work together with " IP-based Determination of a Visitor's Country → ". However, we have one issue with "ip2country", this module work with IPv4 only.

As well the Drupal community has alternative module " Smart IP → " which works with IPv6 fine.

Also, some sites already use "smart_ip" and developers don't want to use both modules at the same time.

I am proposing to add the support for "Smart IP" module too, It isn't a lot of work. And update the description on the module's page.

The patch will be provided.