[networking] ix driver: X520 82599ES SFP+ links fail to establish after boot on FreeBSD 14.2 — ifconfig down/up cycle required

Important notices

• I have read the contributing guidelines at https://github.com/opnsense/core/blob/master/CONTRIBUTING.md
• I am convinced that my issue is new after having checked both open and closed issues

Describe the bug
On OPNsense 26.1.5 (FreeBSD 14.2), an Intel X520 82599ES dual-port SFP+ NIC fails
to establish a physical link after boot, despite the interfaces being present and
hw.ix.unsupported_sfp=1 being correctly set in /boot/loader.conf.local. A manual
ifconfig down/up cycle on the affected interface immediately resolves the issue and
brings the link up at full 10Gbase-SR speed.

Steps to reproduce

1. Install OPNsense 26.1.5 on hardware with an Intel X520 82599ES dual-port SFP+ NIC
2. Insert any non-Intel-branded SFP+ modules (tested: FS.com SFP-10GSR-85, Ubiquiti UACC-OM-MM-10G-D, HP 455885-001)
3. Set hw.ix.unsupported_sfp=1 in /boot/loader.conf.local
4. Connect fibre patch lead between X520 SFP+ port and a 10G switch
5. Reboot
6. Observe: ix0/ix1 show status: no carrier, no link state events in dmesg

Expected behavior
Both ix0 and ix1 should establish link normally after boot without manual intervention.

Actual behavior
Both ports show status: no carrier after every boot. MAC stats show
local_faults incrementing and total_pkts_rcvd accumulating but good_pkts_rcvd: 0.
Running ifconfig ix0 down && sleep 2 && ifconfig ix0 up immediately brings
the link up at 10Gbase-SR full-duplex.

Workaround
rc.syshook script at /usr/local/etc/rc.syshook.d/start/99-ix0-init.sh:
#!/bin/sh
sleep 10
ifconfig ix0 down
sleep 2
ifconfig ix0 up

Boot dmesg (relevant excerpt)
ix0: <Intel(R) X520 82599ES (SFI/SFP+)> ... at device 0.0 on pci1
ix0: Unsupported SFP+ module detected!
ix0: IFDI_ATTACH_PRE failed 5
device_attach: ix0 attach returned 5
ix0: <Intel(R) X520 82599ES (SFI/SFP+)> ... at device 0.1 on pci1
ix0: Using 2048 TX descriptors and 2048 RX descriptors
ix0: Ethernet address: f8:f2:1e:42:df:dd
ix0: eTrack 0x000161c1

Tunable note
hw.ixgbe.unsupported_sfp=1 (old name) is silently ignored on FreeBSD 14.2.
Correct tunable is hw.ix.unsupported_sfp=1. Documentation should be updated.

Version where bug first appeared: OPNsense 26.1.5
Last version where bug did NOT exist: Unknown — first deployment on this hardware

Environment
OPNsense 26.1.5 (amd64) / FreeBSD 14.2
NIC: Intel X520 82599ES (SFI/SFP+) dual port, eTrack 0x000161c1
PCI: vendor=0x8086 device=0x10fb subvendor=0x8086 subdevice=0x0003
SFP+ modules tested: FS.com SFP-10GSR-85, Ubiquiti UACC-OM-MM-10G-D, HP 455885-001
Cable: OM3 50/125 multimode LC UPC duplex
Switch: Ubiquiti Enterprise 8 (10G SFP+ ports)
Hardware: Dell OptiPlex 9020 SFF, Intel i5-4590, 16GB RAM

Start with the ix driver behavior described in the boot dmesg, especially the unsupported-SFP handling and the IFDI_ATTACH_PRE failure, then reproduce the boot failure on an X520 with hw.ix.unsupported_sfp=1. Compare startup with the reported ifconfig down/up workaround; done means both ix0 and ix1 establish 10Gbase-SR link after boot without manual intervention.