e1000e: factor out systim sanitization

This is prepatory work for an expanding list of adapter families that have
occasional ~10 hour clock jumps when being used for PTP. Factor out the
sanitization function and convert to using a feature (bug) flag, per
suggestion from Jesse Brandeburg.

Littering functional code with device-specific checks is much messier than
simply checking a flag, and having device-specific init set flags as needed.
There are probably a number of other cases in the e1000e code that
could/should be converted similarly.

Suggested-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jarod Wilson <jarod@redhat.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/82571.c b/drivers/net/ethernet/intel/e1000e/82571.c
index 7fd4d54..6b03c85 100644
--- a/drivers/net/ethernet/intel/e1000e/82571.c
+++ b/drivers/net/ethernet/intel/e1000e/82571.c
@@ -2032,7 +2032,8 @@
 				  | FLAG2_DISABLE_ASPM_L0S
 				  | FLAG2_DISABLE_ASPM_L1
 				  | FLAG2_NO_DISABLE_RX
-				  | FLAG2_DMA_BURST,
+				  | FLAG2_DMA_BURST
+				  | FLAG2_CHECK_SYSTIM_OVERFLOW,
 	.pba			= 32,
 	.max_hw_frame_size	= DEFAULT_JUMBO,
 	.get_variants		= e1000_get_variants_82571,
@@ -2053,7 +2054,8 @@
 				  | FLAG_HAS_CTRLEXT_ON_LOAD,
 	.flags2			= FLAG2_DISABLE_ASPM_L0S
 				  | FLAG2_DISABLE_ASPM_L1
-				  | FLAG2_NO_DISABLE_RX,
+				  | FLAG2_NO_DISABLE_RX
+				  | FLAG2_CHECK_SYSTIM_OVERFLOW,
 	.pba			= 32,
 	.max_hw_frame_size	= DEFAULT_JUMBO,
 	.get_variants		= e1000_get_variants_82571,