ice: Don't put stale timestamps in the skb

ice: Don't put stale timestamps in the skb

[ Upstream commit 37e738b6fdb14529534dca441e0222313688fde3 ]

The driver has to check if it does not accidentally put the timestamp in
the SKB before previous timestamp gets overwritten.
Timestamp values in the PHY are read only and do not get cleared except
at hardware reset or when a new timestamp value is captured.
The cached_tstamp field is used to detect the case where a new timestamp
has not yet been captured, ensuring that we avoid sending stale
timestamp data to the stack.

Fixes: ea9b847cda64 ("ice: enable transmit timestamps for E810 devices")
Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>