'Determine/extract data associated with the internal port.
When a floating IP is associated with an internal port,
we need to extract/determine some data associated with the
internal port, including the internal_ip_address, and router_id.
The confirmation of the internal port whether owned by the tenant who
owns the floating IP will be confirmed by _get_router_for_floatingip.'

def _get_assoc_data(self, context, fip, floatingip_db):

    (internal_port, internal_subnet_id, internal_ip_address) = self._internal_fip_assoc_data(context, fip, floatingip_db['tenant_id'])
    router_id = self._get_router_for_floatingip(context, internal_port, internal_subnet_id, floatingip_db['floating_network_id'])
    return (fip['port_id'], internal_ip_address, router_id)
