e1000e: fix incorrect link status when switch module pulled

On 82571 with SerDes, the true link state is not always correct when read
from the STATUS register; use existing e1000_has_link() function instead.

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>