ixgbe: call ndo_stop() instead of dev_close() when running offline selftest

Calling dev_close() causes IFF_UP to be cleared which will remove the
interfaces routes and some addresses. That's probably not what the user
intended when running the offline selftest. Besides this does not happen
if the interface is brought down before the test, so the current
behaviour is inconsistent.
Instead call the net_device_ops ndo_stop function directly and avoid
touching IFF_UP at all.

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe.h

@@ -877,6 +877,8 @@ extern const char ixgbe_driver_version[];
 extern char ixgbe_default_device_descr[];
 #endif /* IXGBE_FCOE */
 
+int ixgbe_open(struct net_device *netdev);
+int ixgbe_close(struct net_device *netdev);
 void ixgbe_up(struct ixgbe_adapter *adapter);
 void ixgbe_down(struct ixgbe_adapter *adapter);
 void ixgbe_reinit_locked(struct ixgbe_adapter *adapter);