igb: correct link test not being run when link is down

The igb online link test was always reporting pass because instead of
checking for if_running it was checking for netif_carrier_ok.

This change corrects the test so that it is run if the interface is running
instead of checking for netif carrier ok.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>