igb: fixup AER with proper error handling

Based on Peter Waskiewicz patch for ixgbe.  Add error handling based on
Hemminger's recommendation.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>