ixgbe: reduce PTP Tx timestamp timeout to 1 second

Previously we waited for a whole 15 seconds before we cleared the Tx
timestamp state. This is astronomically long compared to the worst case
timings expected by our devices. In addition, this is longer than the
wait in ptp4l when it detects a fault (caused by missing Tx timestamps).
Thus, reduce the timer to only 1 second, which is well after the maximum
expected delay. This should reduce user frustration when a timestamp
does get dropped for some reason.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>