nfp: TX time stamp packets before HW doorbell is rung

commit 46f1c52e66dbc0d7a99f7c2a3c9debb497fe7b7b upstream.

TX completion may happen any time after HW queue was kicked.
We can't access the skb afterwards.  Move the time stamping
before ringing the doorbell.

Fixes: 4c352362 ("net: add driver for Netronome NFP4000/NFP6000 NIC VFs")
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>