e1000: no need auto-negotiation if link was down

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: NJason Wang <jasowang@redhat.com>
Signed-off-by: NAmos Kong <akong@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/e1000.c

@@ -166,6 +166,11 @@ static void
 set_phy_ctrl(E1000State *s, int index, uint16_t val)
 {
     if ((val & MII_CR_AUTO_NEG_EN) && (val & MII_CR_RESTART_AUTO_NEG)) {
+        /* no need auto-negotiation if link was down */
+        if (s->nic->nc.link_down) {
+            s->phy_reg[PHY_STATUS] |= MII_SR_AUTONEG_COMPLETE;
+            return;
+        }
         s->nic->nc.link_down = true;
         e1000_link_down(s);
         s->phy_reg[PHY_STATUS] &= ~MII_SR_AUTONEG_COMPLETE;