RFC8345 defines ietf-network(-topology), which we should adopt

OpenDaylight uses ietf-topology as one of the central models. This model has finally been standardized as ietf-network and ietf-network-topology.

We need to drive adoption of this model in four key areas:

• NETCONF, https://git.opendaylight.org/gerrit/73661
• OVSDB, which should mirror NETCONF by my estimate
• BGPCEP, which needs to find suitable replacements for draft isis/ospf topology
• OpenFlow world, which is using ietf-topology through opendaylight-topology

This obviously impacts our NBI, but the differences are largely mechanic.