_get_container_ifname only names the kernel interface inside the
container's network namespace (single call site: docker move_to_ns) -
IOL never uses that path, and the controller port list never reads it.
Name the ports through the template's custom_adapters instead (the
mechanism SR Linux appliances use for mgmt0/e1-1): adapter N shows as
Ethernet{N/4}/{N%4}, matching the IOS CLI, with no server-side changes.
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