ixgbe: fix LED blink logic to check for link

Previously the driver would force link without checking whether the link was
already established. This caused some inconsistencies in the LED blink rate.

Do not force link if link is already up.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>