Allow setting loopback as direct routing device in Cilium 1.15+

[robertvolkmann]

How to categorize this PR? /area networking /kind api-change

What this PR does / why we need it: Since Cilium 1.15, the loopback device will be no longer autodetected as direct routing device and has to be manually configured. https://github.com/cilium/cilium/issues/30889 https://github.com/cilium/cilium/pull/31200

Special notes for your reviewer:

• The struct Nodeport in types_network looks unused.
• For reference: Cilium documentation regarding devices and directRoutingDevice

[gardener-prow[bot]]

Hi @robertvolkmann. Thanks for your PR.

I'm waiting for a gardener member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[gardener-robot]

@robertvolkmann Thank you for your contribution.

[gardener-robot-ci-3]

Thank you @robertvolkmann for your contribution. Before I can start building your PR, a member of the organization must set the required label(s) {'reviewed/ok-to-test'}. Once started, you can check the build status in the PR checks section below.

[axel7born]

/ok-to-test

[axel7born]

The change looks good in general. Only, I would formulate the comment a bit different.

[axel7born]

/lgtm