Background:
Cilium currently requires a v5.10-equivalent kernel. Meaning it fatals on startup if certain v5.10-level BPF features are not available.

Upstream will stop providing updates for the v5.10 and v5.15 kernel releases by end of 2026. Let's start moving Cilium to a more modern kernel requirement, so that we can reduce our test footprint and depend on infrastructure that's available in newer kernels.

Previous efforts were in #39150 and #30456.

Bumping the minimum requirement to a v6.1 kernel would affect:

• Amazon AL2 (EOL June 2026)
• Debian Bullseye (EOL August 2026)
• RHEL 8
• Ubuntu 22.04 (defaulted to a v5.15 kernel, but has newer options)
• Old Bottlerocket (?)

RHEL9 uses a v5.14 kernel as baseline, but should have sufficient BPF backports to stay compatible (RHEL 9.4 comes with a 6.6 BPF stack).

Proposal:
With the v1.20 release (Summer 2026), bump Cilium's kernel requirement to v6.1. Users who are still interested in running a near-EOL kernel for the last 6 months of its life are welcome to keep using Cilium v1.19.