ixgbe: prevent link checks while resetting

It some situations the driver sets __IXGBE_RESETTING and then
__IXGBE_DOWN flags. It is possible a link check may sneak in
between.

This patch adds check for both flags.
The idea is to reduce register reads while the PHY is resetting.

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>