cfg: New API to get extended node/link infomation

Current we horribly over-use totempg_ifaces_get() to
retrieve information about knet interfaces. This is an attempt to
improve on that.

All transports are supported (so not only Knet but also UDP(U)).

This patch builds best against the "onwire-upgrade" branch of knet
as that's what sparked my interest in getting more information out.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>