Update kernel to include network capabilities

[sjmiller609]

Note

Add new kernel version 20251211, make it the default, and provide its download URLs.

• Kernel versions (lib/system/versions.go):
  • Add Kernel_20251211 and its download URLs for x86_64 and aarch64.
  • Set DefaultKernelVersion to Kernel_20251211.
  • Include Kernel_20251211 in SupportedKernelVersions.

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