fix: prevent static IP assignment matching subnet gateway

[kavirakesh14]

What does this PR do?

This adds a validation step to the Netavark IPAM logic to immediately reject static IP requests that conflict with the subnet's gateway IP.

Previously, if a container was started with a static IP matching the gateway, Netavark would accept it. The container would start successfully but suffer from silent internal networking failures, specifically resulting in "connection refused" errors on internal sockets.

By failing fast inside allocIPs with an "address already in use" error, Podman's behavior now mirrors Docker's standard behavior and prevents this ghost networking state.

Fixes Issue

Fixes podman-container-tools/podman#28863

How was this tested?

• Compiled containers/common locally and linked it to a fresh build of Podman.
• Passed local go fmt, go vet, and go test.

[Luap99]

Thanks, code wise this seems fine but please add a test case https://github.com/podman-container-tools/container-libs/blob/main/common/libnetwork/netavark/ipam_test.go

Also from your commit message please drop "Committer: kavirakesh14 kavirakesh007@gmail.com" That is not a valid/normal trailer.

And for the sign off and git author is it generally expected to use the real name
https://github.com/podman-container-tools/container-libs/blob/main/CONTRIBUTING.md#sign-your-prs

Use a real name (sorry, no anonymous contributions). A real name does not require a legal name, nor a birth name, nor any name that appears on an official ID (e.g. a passport). Your real name is the name you convey to people in the community for them to use to identify you as you. The key concern is that your identification is sufficient enough to contact you if an issue were to arise in the future about your contribution.

Though that is not a strict requirement and I think using the github id is fine.

[kavirakesh14]

Thanks for the review! @Luap99, I Added the test case and dropped the Committer: trailer.

[Luap99]

LGTM