Lease state dictates install or remove

Rely on lease state passed in from __ni_system_interface_update_lease()
to determine installation/removal of lease information from the system.
Additionally check the seqno of lease to only install the lease of
interest on update/new lease arrival.
[system_update] Streamline lease updates

- Perform updates as leases are passed to us from ifconfig.c:__ni_system_interface_update_lease().
- Don't disable an updater if an error during install/remove occurs.