IPVPN: adaptations for LB/CHSO and per-endpoint RDs
IPVPN: adaptations for LB/CHSO and per-endpoint RDs

Advertise/withdraw or re-advertise BGP routes based on each endpoint
route distinguisher and consistent hash sort order.

Advertise/withdraw FlowSpec routes, based on route leaking mechanism,
when VPNInstance has only one endpoint.

Factorize code to start/stop traffic redirection to VPNInstance.

openstack/networking-bagpipe,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe,stackforge/networking-bagpipe-l2,openstack/networking-bagpipe-l2,openstack/networking-bagpipe-l2