i40e: use same check for Rx hang as for Rx timestamps

It's possible that the user configured only Tx hardware timestamping,
and thus we might be receiving PTP traffic which we timestamp but which
software never reads. In this case we don't want to check for Rx
timestamp hang, because we already know that software won't be handling
them. Thus, we add the same check against pf->ptp_rx as we have in the
Rx timestamp code path.

Change-ID: I66486c8dba307facbff8eace4e52e2f083789d1b
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>