Discover interface LACP status

We call self._get_lacp_data() to read the device interface LACP membership, if any. This info comes from the LAG MIB.

First, we read dot3adAggActorAdminKey. This gives us the ifIndex for any aggregate interfaces that exists (aka Bridge-Aggregation, PortChannel, etc.)

If we find aggregate interfaces, then we walk dot3adAggPortActorAdminKey.

This gets the admin key or “index” for physical member interfaces. This maps back to the logical or actor aggregates above in dot3adAggActorAdminKey