Fix logic for multi-node CNI warning.

[toddliebenschutz-jones]

Fixes #19665

This PR fixes the logic for the warning Cluster was created without any CNI, adding a node to it might cause broken networking. which should be shown when adding a second node to a single-node cluster created without CNI.

The warning log was added in #9875 in response to this comment thread #9875 (comment). The proposed solution was:

We set and store a cluster config something like CreatedWithMultiNode bool true whenever user provides --node > 1. And we use this value to decide the CNI between KindNet and Disabled. And when a cluster is created with only control plane node and a node is added later, we show a warning that multi node networking might be broken (if it is not reconfigured already).

The warning should be shown when (1) the cluster is created with only a control plane node, and (2) CNI is not configured already. The corresponding change erroneously used an or instead of and.

Output diff

Before:

➜  minikube out/minikube start   
😄  minikube v1.38.1 on Darwin 26.3.1 (arm64)
✨  Automatically selected the docker driver
❗  Starting v1.39.0, minikube will default to "containerd" container runtime. See #21973 for more info.
📌  Using Docker Desktop driver with root privileges
👍  Starting "minikube" primary control-plane node in "minikube" cluster
🚜  Pulling base image v0.0.50-1772266598-22719 ...
🔥  Creating docker container (CPUs=2, Memory=8100MB) ...
🐳  Preparing Kubernetes v1.35.1 on Docker 29.2.1 ...
🔗  Configuring bridge CNI (Container Networking Interface) ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🌟  Enabled addons: default-storageclass, storage-provisioner
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

➜  minikube out/minikube node add
😄  Adding node m02 to cluster minikube as [worker]
❗  Cluster was created without any CNI, adding a node to it might cause broken networking.
👍  Starting "minikube-m02" worker node in "minikube" cluster
🚜  Pulling base image v0.0.50-1772266598-22719 ...
🔥  Creating docker container (CPUs=2, Memory=2200MB) ...
🐳  Preparing Kubernetes v1.35.1 on Docker 29.2.1 ...
🔎  Verifying Kubernetes components...
🏄  Successfully added m02 to minikube!

After:

➜  minikube out/minikube start   
😄  minikube v1.38.1 on Darwin 26.3.1 (arm64)
✨  Automatically selected the docker driver
❗  Starting v1.39.0, minikube will default to "containerd" container runtime. See #21973 for more info.
📌  Using Docker Desktop driver with root privileges
👍  Starting "minikube" primary control-plane node in "minikube" cluster
🚜  Pulling base image v0.0.50-1772266598-22719 ...
🔥  Creating docker container (CPUs=2, Memory=8100MB) ...
🐳  Preparing Kubernetes v1.35.1 on Docker 29.2.1 ...
🔗  Configuring bridge CNI (Container Networking Interface) ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🌟  Enabled addons: storage-provisioner, default-storageclass
🏄  Done! kubectl is now configured to use "minikube" cluster and "default" namespace by default

➜  minikube out/minikube node add
😄  Adding node m02 to cluster minikube as [worker]
👍  Starting "minikube-m02" worker node in "minikube" cluster
🚜  Pulling base image v0.0.50-1772266598-22719 ...
🔥  Creating docker container (CPUs=2, Memory=2200MB) ...
🐳  Preparing Kubernetes v1.35.1 on Docker 29.2.1 ...
🔎  Verifying Kubernetes components...
🏄  Successfully added m02 to minikube!

[k8s-ci-robot]

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This pull-request has been approved by: toddliebenschutz-jones
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[k8s-ci-robot]

Hi @toddliebenschutz-jones. Thanks for your PR.

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[minikube-bot]

Can one of the admins verify this patch?