fix(netwotk): Get MTU from tap device and set it in Qemu and clh args

[cmainas]

Description

Qemu and Cloud hypervisor support setting the MTU value in the command line arguments of the network device. Therefore, get the MTU value from the network interface of the host that we associate with the tap device and set it as the MTU for Qemu's and cloud hypervisor's virtio network device.

Related issues

Related to #547 but since Firecracker does not accept any option to set the MTU or to retrieve it form the tap device, the issue will remain open.

How was this tested?

In a k3s environment using flannel, which uses 1450 for MTU, qemu and clh based images where deployed and checked the MTUs of the network interface inside the VM.

e.g. for a pod configuration:

    spec:
      runtimeClassName: urunc
      containers:
      - image: harbor.nbfc.io/nubificus/urunc/busybox-cloud-hypervisor-linux-raw:latest
        args: ["ip", "a"]

LLM usage

N/A

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint).
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl).
• If LLMs were used: I have read the llm policy.

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[ananos]

thanks @cmainas! looks good -- just a note for future reference, FC support is under way, pending merge of firecracker-microvm/firecracker#5828.

Solo5 should detect that, I believe we have raised that in Solo5/solo5#605 and should be resolved after: Solo5/solo5#606