netdev driver should report the real state through netdev_carrier_on/netdev_carrier_off correctly

Please see the discussion here: https://github.com/apache/incubator-nuttx/pull/5049

Start with the discussion in pull request 5049, which is the only location linked by the issue. Trace how the netdev driver reports carrier state through netdev_carrier_on and netdev_carrier_off, then verify that the reported state matches the real device state. The issue does not name a file or test, so the relevant driver and validation steps must be identified from that discussion.

Written by the indexing model from the issue text.