bnxt_en: Update firmware call to retrieve TX PTP timestamp

New firmware interface requires the PTP sequence ID header offset to
be passed to the firmware to properly find the matching timestamp
for all protocols.

Fixes: 83bb623c ("bnxt_en: Transmit and retrieve packet timestamps")
Reviewed-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>