NMT-1521: Add per interface ipv4 forwarding test.

[emy]

Is this a BUG FIX or a FEATURE ?:

Uncomment only one, leave it on its own line:

/kind bug

/kind enhancement

What this PR does / why we need it:
As discussed with @qinqon we're introducing an example test for per interface ipv4 forwarding.

Special notes for your reviewer:

Release note:

NONE

Summary by CodeRabbit

• Documentation
  • Added a new example manifest demonstrating per-interface IPv4 forwarding using a NodeNetworkConfigurationPolicy. The example targets interface eth1, sets it up, enables IPv4 with DHCP, and turns on forwarding.
• Tests
  • Expanded example coverage by adding a corresponding test entry for the new per-interface IPv4 forwarding example.

[coderabbitai]

Walkthrough

Adds a new example manifest for a NodeNetworkConfigurationPolicy enabling IPv4 forwarding on eth1, and registers this example in the test examples list. No other files or behaviors are modified.

Changes

Cohort / File(s)	Summary
New example manifest docs/examples/per-interface-ipv4-forwarding.yaml	Adds a NodeNetworkConfigurationPolicy example named per-interface-ipv4-forwarding configuring eth1 (ethernet, up) with IPv4 DHCP enabled and forwarding true.
Test examples registry update test/doc/examples.go	Adds an ExampleSpec entry: name "Per interface IPv4 forwarding", file "per-interface-ipv4-forwarding.yaml", policy "per-interface-ipv4-forwarding", ifaceNames ["eth1"].

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

I hop through YAML fields so bright,
eth1 wakes, its flags alight—
DHCP whispers, routes take wing,
Forward, packets! Spring to spring.
In tests we note this tidy feat,
A carrot checkmark: crisp and neat. 🥕

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title "NMT-1521: Add per interface ipv4 forwarding test." clearly and concisely summarizes the primary change—adding a per‑interface IPv4 forwarding test/example—and includes the tracking ticket; this matches the added example manifest and test registration in the PR.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

• 📝 Generate Docstrings

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment

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[kubevirt-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign cybertron for approval. For more information see the Code Review Process.

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

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[coderabbitai]

Actionable comments posted: 2

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between c85fc6e and c656ecb.

📒 Files selected for processing (2)

• docs/examples/per-interface-ipv4-forwarding.yaml (1 hunks)
• test/doc/examples.go (1 hunks)

[qinqon]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a new example and a corresponding test for configuring per-interface IPv4 forwarding. The changes are clear and well-contained. My review includes one suggestion for the new example YAML file to improve its conciseness by removing a redundant property, which will help align it with best practices for users who might copy this example.

[qinqon]

@emy looks like like the upgrade test fail at the test ?

[mkowalski]

But it's not only that failing... I see also

   Error from server (NotFound): nodenetworkconfigurationpolicies.nmstate.io "dns" not found
  [FAILED] 
  Unexpected error:
      <*errors.errorString | 0xc000698ec0>: 
      ./cluster/kubectl.shwait nncp dns --for condition=Available --timeout 3m : selecting podman as container runtime
      Error from server (NotFound): nodenetworkconfigurationpolicies.nmstate.io "dns" not found
       exit status 1
      {
          s: "./cluster/kubectl.shwait nncp dns --for condition=Available --timeout 3m : selecting podman as container runtime\nError from server (NotFound): nodenetworkconfigurationpolicies.nmstate.io \"dns\" not found\n exit status 1",
      }
  occurred 

as well as

   Error from server (NotFound): nodenetworkconfigurationpolicies.nmstate.io "linux-bridge-vlan" not found
  [FAILED] 
  Unexpected error:
      <*errors.errorString | 0xc000bbcd00>: 
      ./cluster/kubectl.shwait nncp linux-bridge-vlan --for condition=Available --timeout 3m : selecting podman as container runtime
      Error from server (NotFound): nodenetworkconfigurationpolicies.nmstate.io "linux-bridge-vlan" not found
       exit status 1
      {
          s: "./cluster/kubectl.shwait nncp linux-bridge-vlan --for condition=Available --timeout 3m : selecting podman as container runtime\nError from server (NotFound): nodenetworkconfigurationpolicies.nmstate.io \"linux-bridge-vlan\" not found\n exit status 1",
      } 

[mkowalski]

/retest

[kubevirt-bot]

@emy: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubernetes-nmstate-e2e-upgrade-k8s	c656ecb	link	false	/test pull-kubernetes-nmstate-e2e-upgrade-k8s

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