e1000e: prevent oops when adapter is being closed and reset simultaneously

When the adapter is closed while it is simultaneously going through a
reset, it can cause a null-pointer dereference when the two different code
paths simultaneously cleanup up the Tx/Rx resources.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/ethernet/intel/e1000e/e1000.h b/drivers/net/ethernet/intel/e1000e/e1000.h
index 86cdd47..b83897f 100644
--- a/drivers/net/ethernet/intel/e1000e/e1000.h
+++ b/drivers/net/ethernet/intel/e1000e/e1000.h
@@ -161,6 +161,12 @@
 /* Time to wait before putting the device into D3 if there's no link (in ms). */
 #define LINK_TIMEOUT		100
 
+/*
+ * Count for polling __E1000_RESET condition every 10-20msec.
+ * Experimentation has shown the reset can take approximately 210msec.
+ */
+#define E1000_CHECK_RESET_COUNT		25
+
 #define DEFAULT_RDTR			0
 #define DEFAULT_RADV			8
 #define BURST_RDTR			0x20