- Each stp port is added sequentially so it was possible for our bridgeid to
change every time because the new port has a lower MAC address. Instead
just find the lowest MAC address from all Ethernet adapters in the machine
as the value only needs to be unique, this stops a lot of churn on the
protocol.
- Update the states after enabling or disabling a port.
- Keep tabs if we have been stopped or started by our parent bridge.
- The callout only needs to be drained before destroying the mutex, move it to
bstp_detach.