ClosNetwork: refine links management

* CNSwitch
Only unset is_active, leave it up to derived classes to set: leaves set
upon barrier reply once, spines manage the attribute to depend on all
downlink ports being up.

* CNSpineSwitch
Dismiss in_service, call handleDownlinkAdded() only after the barrier
reply.

* CNLeafSwitch
Request uplinks status after barrier reply.

* Topology
Dismiss linkIsUp(), which inboundPorts() used to filter its results. Add
necessary filtering (by is_connected or is_ready) into functions that
use inboundPorts(). Implement "loadUplinks" message.
ClosNetwork: dismiss two methods