Associate the load balancer to the logical router to which the VIP network is attached to

[Numan Siddique]

Suppose a load balancer - LB1 is created with vip ip - 'VIP' belonging to a network - NET1. Presently there is a limitation with OVN loadbalancer. Another VM belonging to same network NET1 cannot connect to the VIP unless the NET1 is attached to a router. This is because, when the VM sends an ARP request for the VIP, it gets no ARP reply. Since the VIP port will be down ovn-northd doesn't add any ARP reply flow for the VIP. But when the NET1 is associated to a router, the logical router pipeline adds the ARP reply flows and it replies to the ARP request for the VIP with the router's MAC if the load balancer LB1 is associated to the logical router R1 (example: ovn-nbctl lb-lr-add LB1 LR1)

Presently the OVN octavia driver, associates the load balancer to the router when the load balancer is created if the VIP network of the load balancer is connected to a router. But it doesn't handle the other case when the VIP network is associated to the router after the load balancer is created.
OVN provider driver should listen to the appropriate events (using ovsdbapp) so that it gets notified when the VIP network is associated to the router and when it is notified, it should associate the load balancer with the logical router.