netinfo: remove unused getipv6addrs

In 5fa87504543719fdc827d2284738a7723b8a5973 we started using libnl
to retrieve both ipv4 and ipv6 addresses and this method fell into
deprecation. It's time to get rid of this unused code.

Change-Id: I4ce3631185f44574454e240eb62bf659c4528c81
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29599
Reviewed-by: Dan Kenigsberg <danken@redhat.com>