[ixpmanager] as112 config kernel export ipv6

[Pete Ashdown]

I'm finding my as112 server has no idea how to get back to the IPv6 
prefixes of peers. I noticed this in the generated bird config:

protocol kernel {
     ipv4 {
         export all;
     };
     scan time 60;
}

Should it be ipv6?  The "Protocol" for the router is properly set to 
"ipv6" and the rest of the config has the proper IP addresses of the 
route servers.

The "known good" sample configuration isn't explicit for ipv4 in the 
export stanza:

https://github.com/inex/IXP-Manager/blob/master/data/travis-ci/known-good/ci-apiv4-as112-lan1-ipv6.conf