Linux kernel forbids to add VRF (layer 3) devices into OVS bridges
(layer 2). This patch changes the approach to link EVPN/VRF to OVS
bridges by using a veth-pair instead, or a vlan device for the
provider vlan networks use case.
It also fixes the next:
- typo on function definition "disconnect_evpn_to_ovn", changed by
"disconnect_evpn_from_ovn"
- avoid code duplication to expose subnets, by making an auxiliar
function that can be reused by the reconciliation loop too.
Change-Id: Iccd1b01014bf026c07e39f48e8aa234a9a303877
5ba2f40262