bnxt_en: Implement ethtool_ops -> get_link_ext_state()

bnxt_en: Implement ethtool_ops -> get_link_ext_state()

Map the link_down_reason from the FW to the ethtool link_ext_state
when it is available.  Also log it to the link down dmesg when it is
available.  Add 2 new link_ext_state enums to the UAPI:

ETHTOOL_LINK_EXT_STATE_OTP_SPEED_VIOLATION
ETHTOOL_LINK_EXT_STATE_BMC_REQUEST_DOWN

to cover OTP (one-time-programmable) speed restrictions and
BMC (Baseboard management controller) forcing the link down.

Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://patch.msgid.link/20260108183521.215610-7-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>