topo: skip creating empty meshnet Topology CR for nodes with no links (#26)

When a node has no Links in its meshnet TopologySpec, kne currently
still creates a `Topology` CR with `spec: {}`. meshnetd's
`Get(podName)` RPC then reads the CR, fails the
`unstructured.NestedSlice(... "spec", "links")` lookup with
`!found`, logs `could not find 'Link' array in pod's spec` and
returns an empty Pod struct. The CNI plugin sees `NodeIp == ""`
and aborts the sandbox with the (misleading) error:

    plugin type="meshnet" failed (add):
      meshnetd provided no HOST_IP address:  or HOST_INTF:

Every pod scheduled on a node with no links is then stuck in
FailedCreatePodSandBox loops until kubelet's 4-minute deadline.

Skip the CR creation for unconnected nodes. The meshnet CNI plugin
already handles "no Topology CR for this pod" gracefully
(plugin/meshnet.go cmdAdd treats Get error as `not a topology pod
returning`) and chains through to the next plugin, so the result
is the same as for any other workload on the cluster.

This is a no-op for topologies whose nodes all have links and
significantly improves robustness for sparse/scale-test topologies
where some nodes are intentionally isolated.

Co-authored-by: dn <dn@msupino-dev>

Author: msupinodn

topo/topo.go

@@ -554,6 +554,19 @@ func (m *Manager) topologySpecs(ctx context.Context) ([]*topologyv1.Topology, er
 	// replace node name with pod name, for peer pod attribute in each link
 	for nodeName, specs := range nodeSpecs {
 		for _, spec := range specs {
+			// Skip Topology CRs with no links: meshnetd's Get RPC
+			// treats a missing `spec.links` field as an error
+			// (`could not find 'Link' array in pod's spec`) and the
+			// CNI plugin then aborts pod sandbox creation with a
+			// misleading `meshnetd provided no HOST_IP` message.
+			// For unconnected nodes we simply don't create the CR;
+			// the meshnet CNI plugin already handles "no Topology
+			// CR" gracefully and falls through to the next plugin
+			// in the chain.
+			if len(spec.Spec.Links) == 0 {
+				log.V(1).Infof("Skipping empty Topology spec for node %s (no links)", nodeName)
+				continue
+			}
 			for l := range spec.Spec.Links {
 				link := &spec.Spec.Links[l]
 				peerSpecs, ok := nodeSpecs[link.PeerPod]