Fix default value for standalone tests

[floryut]

What type of PR is this?
/kind failing-test

What this PR does / why we need it:
Default value for tests are needed (ipip was wrong and should default to true, network_plugin might not be set)

Which issue(s) this PR fixes:
Error in CI

fatal: [530113196-k8s-node-nf-1]: FAILED! => {"msg": "The conditional check 'kube_network_plugin == 'flannel'' failed. The error was: error while evaluating conditional (kube_network_plugin == 'flannel'): 'kube_network_plugin' is undefined\n\nThe error appears to be in '/builds/kargo-ci/kubernetes-sigs-kubespray/tests/testcases/040_check-network-adv.yml': line 17, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n tasks:\n - name: Flannel | Disable tx and rx offloading on VXLAN interfaces (see https://github.com/coreos/flannel/pull/1282)\n ^ here\n"}
...ignoring

Special notes for your reviewer:
roles\network_plugin\calico\defaults\main.yml:10 -> ipip: true

Does this PR introduce a user-facing change?:

NONE

[Miouge1]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floryut, Miouge1

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [Miouge1]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment