bnxt_en: replace ptp_lock with irqsave variant

In netpoll configuration the completion processing can happen in hard
irq context which will break with spin_lock_bh() for fullfilling RX
timestamp in case of all packets timestamping. Replace it with
spin_lock_irqsave() variant.

Fixes: 7f5515d1 ("bnxt_en: Get the RX packet timestamp")
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Message-ID: <20241016195234.2622004-1-vadfed@meta.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>