'Disassociate all floating IPs linked to specific port.
@param port_id: ID of the port to disassociate floating IPs.
@param do_notify: whether we should notify routers right away.
@return: set of router-ids that require notification updates
if do_notify is False, otherwise None.'

def disassociate_floatingips(self, context, port_id, do_notify=True):

    router_ids = super(L3_NAT_db_mixin, self).disassociate_floatingips(context, port_id, do_notify)
    if do_notify:
        self.notify_routers_updated(context, router_ids)
        return
    return router_ids
