When the OS driver enables/disables the port, go ahead and set the port's
link status to up/down in response to the change.  This more closely
emulates real hardware when the PHY for the port is brought up/down
and the PHY negotiates carrier (link status) with link partner.  In
the case of qemu, the virtual rocker device can't really do link
negotiation with the link partner as that requires signally over a
physical medium (the wire), so just pretend the negotiation was
successful and bring the link up when the port is enabled.

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1433985681-56138-4-git-send-email-sfeldma@gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>