cli: improve 'show interfaces' to list container networks

[troglobit]

Take this example:

admin@infix-00-00-00:/> show interfaces 
INTERFACE       PROTOCOL   STATE       DATA
---------------------------------------------------------------------
lo              ethernet   UP          00:00:00:00:00:00
                ipv4                   127.0.0.1/8 (static)
                ipv6                   ::1/128 (static)
br0             bridge
│               ethernet   UP          02:00:00:00:00:00
│               ipv4                   169.254.1.3/16 (random)
│               ipv4                   192.168.122.160/24 (dhcp)
├ e1            bridge     FORWARDING
└ veth0b        bridge     FORWARDING
veth0a          ethernet
veth0b          ethernet   UP          32:ed:2e:8b:17:9f

A simple setup with a bridge and a VETH pair. One end of the VETH pair is set as bridge port, but where's the other one?

Could it be in a container?

admin@infix-00-00-00:/> exit
admin@infix-00-00-00:~$ sudo container --net veth0a locate
system

There it was!

---

Proposed output:

admin@infix-00-00-00:/> show interfaces 
INTERFACE       PROTOCOL   STATE       DATA
---------------------------------------------------------------------
lo              ethernet   UP          00:00:00:00:00:00
                ipv4                   127.0.0.1/8 (static)
                ipv6                   ::1/128 (static)
br0             bridge
│               ethernet   UP          02:00:00:00:00:00
│               ipv4                   169.254.1.3/16 (random)
│               ipv4                   192.168.122.160/24 (dhcp)
├ e1            bridge     FORWARDING
└ veth0b        bridge     FORWARDING
veth0a          ethernet               container:system
veth0b          ethernet   UP          32:ed:2e:8b:17:9f

More information about a running container's network interfaces can be dumped using sudo podman inspect system | jq -r '.[].NetworkSettings.Networks. Unfortunately that command does not list the name of the interfaces inside the container. For that nsenter is needed, then inspecting all interfaces and comparing their ifname to their ifalias.