Commit b9d03e35 added link
auto-negotiation emulation, it would always set link up by
callback function. Problem exists if original link status
was down, link status should not be changed in auto-negotiation.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>