tx_hwtstamp_skb is always set before work is scheduled,
work is cancelled before tx_hwtstamp_skb is set to NULL.
PTP work cannot ever see tx_hwtstamp_skb set to NULL.
Signed-off-by: NJakub Kicinski <kubakici@wp.pl>
Tested-by: NAaron Brown <aaron.f.brown@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>