e1000e: 82571 check for link fix on 82571 serdes

Check for link test does not work properly for 82571 parts in a blade
environment with an unterminated serdes link partner.  Make the test more
robust by checking the invalid bit.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>