ncsi: Propagate carrier gain/loss events to the NCSI controller

Report the carrier/no-carrier state for the network interface
shared between the BMC and the passthrough channel. Without this
functionality the BMC is unable to reconfigure the NIC in the event
of a re-cabling to a different subnet.

Signed-off-by: Johnathan Mantey <johnathanx.mantey@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>