[Intel-wired-lan] [iwl-net v2 2/2] igb: Fix missing time sync events

[Daiwei Li]

Hi,

It appears this change breaks PTP on the 82580 controller, as ptp4l reports:

> timed out while polling for tx timestamp increasing tx_timestamp_timeout or
> increasing kworker priority may correct this issue, but a driver bug likely
> causes it

The 82580 controller has a hardware bug in which reading TSICR doesn't clear
it. See this thread
https://lore.kernel.org/all/CDCB8BE0.1EC2C%25matthew.vick@intel.com/ where the
bug was confirmed by an Intel employee. Any chance we could add back the ack
for 82580 specifically? Thanks!