e1000: return PCI_ERS_RESULT_DISCONNECT on permanent error

PCI drivers that implement the io_error_detected callback
should return PCI_ERS_RESULT_DISCONNECT if the state
passed in is pci_channel_io_perm_failure.  This state is
not checked in many of the network drivers.

The patch fixes the omission in the e1000 driver.

Based on Mike Mason's similar patch for e1000e.

Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
CC: Mike Mason <mmlnx@us.ibm.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>