device interface: support port channel member assignment and min-links on-chain

[thijsvanemmerik]

When registering a port channel interface on-chain, contributors currently have no way to associate the physical member interfaces with that port channel, or to configure operational parameters like min-links.

Requested changes

1. Member interface linking — allow physical interfaces (e.g. Ethernet1/1, Ethernet2/1) to be associated with a port channel on-chain, so the relationship is visible and verifiable.
2. min-links — add an optional --min-links <n> field to port channel registration. This defines the minimum number of active member links required for the port channel to remain up. For example, a port channel with 8 members and --min-links 4 will go down if fewer than 4 links are active.

Why

This information is currently only configured on the device itself and not reflected on-chain, reducing operational transparency and the ability to verify contributor topology.