igc: Retrieve TX timestamp during interrupt handling
When the interrupt is handled, the TXTT_0 bit in the TSYNCTXCTL
register should already be set and the timestamp value already loaded
in the appropriate register.
This simplifies the handling, and reduces the latency for retrieving
the TX timestamp, which increase the amount of TX timestamps that can
be handled in a given time period.
As the "work" function doesn't run in a workqueue anymore, rename it
to something more sensible, a event handler.
Using ntpperf[1] we can see the following performance improvements:
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com> Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de> Tested-by: Naama Meir <naamax.meir@linux.intel.com> Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>