e1000e: 82571 Serdes can fail to get link

When link partner is sending continuous Config symbols, the 82571 Serdes
FIFO can overflow resulting in Invalid bit getting set.  To resolve this,
if Sync and Config bits are both 1 ignore the Invalid bit and restart
auto-negotiation.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Emil Tantilov <emil.s.tantilov@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>