bnxt_en: improve TX timestamping FIFO configuration

bnxt_en: improve TX timestamping FIFO configuration

Reconfiguration of netdev may trigger close/open procedure which can
break FIFO status by adjusting the amount of empty slots for TX
timestamps. But it is not really needed because timestamps for the
packets sent over the wire still can be retrieved. On the other side,
during netdev close procedure any skbs waiting for TX timestamps can be
leaked because there is no cleaning procedure called. Free skbs waiting
for TX timestamps when closing netdev.

Fixes: 8aa2a79e9b95 ("bnxt_en: Increase the max total outstanding PTP TX packets to 4")
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Link: https://patch.msgid.link/20250424125547.460632-1-vadfed@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>