Change

This change adds cilium-dbg commands to manage multicast BPF maps.

Following commands are added

- cilium-dbg bpf multicast group list
- cilium-dbg bpf multicast group add <group>
- cilium-dbg bpf multicast group delete <group>
- cilium-dbg bpf multicast subscriber list <group|all>
- cilium-dbg bpf multicast subscriber add <group> <subscriber>
- cilium-dbg bpf multicast subscriber delete <group> <subscriber>

This is follow up of #29469
Feature tracking issue #13239

Enabling Multicast

Users can configure multicast maps sub-system to enable multicast connectivity in the cluster. Following configuration will be required to achieve this.

• Enable multicast using cilium-cli
  cilium config set multicast-enabled true

  -- This will result in cilium pod restart.
  -- Cilium MUST be configured in vxlan tunnel mode.

• For each cilium pod, configure desired multicast groups.
  cilium-dbg multicast group add <group IP>

• Configure group subscriber map to add all nodes (except self) as remote subscribers.
  cilium-dbg multicast subscriber add <groupIP> <SubscriberIP>

  -- Cilium node internal IP can be found using kubectl get ciliumnodes.cilium.io command.
  -- Use internal IPs as subscriber IPs.
  -- Omit self node IP from adding as subscriber.

After doing this, multicast receiver pods can send out IGMP join and multicast sender pods can start sending multicast stream.

multicast: add CLIs to manage multicast BPF maps