missing hw.em.msix support in FreeBSD 14.0-CURRENT?

Hello,

I am using this em(4) driver for some tests. According to the man page
below, there should be a "hw.em.msix" sysctl to enable/disable MSI-X style
interrupts. But why is it missing in my system below?
https://man.freebsd.org/cgi/man.cgi?em(4)

root@s1:~ # dmesg | egrep "8254"
Timecounter "i8254" frequency 1193182 Hz quality 0
Event timer "i8254" frequency 1193182 Hz quality 100
em0: <Intel(R) Legacy PRO/1000 MT 82541GI> port 0xdcc0-0xdcff mem
0xdfae0000-0xdfafffff irq 64 at device 7.0 on pci6
em1: <Intel(R) Legacy PRO/1000 MT 82541GI> port 0xccc0-0xccff mem
0xdf8e0000-0xdf8fffff irq 65 at device 8.0 on pci7
em2: <Intel(R) Legacy PRO/1000 MT 82546EB (Copper)> port 0xbcc0-0xbcff mem
0xdf5e0000-0xdf5fffff irq 106 at device 4.0 on pci9
em3: <Intel(R) Legacy PRO/1000 MT 82546EB (Copper)> port 0xbc80-0xbcbf mem
0xdf5c0000-0xdf5dffff irq 107 at device 4.1 on pci9
em4: <Intel(R) Legacy PRO/1000 MT 82546EB (Copper)> port 0xacc0-0xacff mem
0xdf3e0000-0xdf3fffff irq 101 at device 3.0 on pci10
em5: <Intel(R) Legacy PRO/1000 MT 82546EB (Copper)> port 0xac80-0xacbf mem
0xdf3c0000-0xdf3dffff irq 102 at device 3.1 on pci10

root@s1:~ # ifconfig em5
em5: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
options=481009b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,VLAN_HWFILTER,NOMAP>
ether 00:04:23:b7:1e:1d
inet 10.1.1.2 netmask 0xffffff00 broadcast 10.1.1.255
media: Ethernet 1000baseT <full-duplex>
status: active
nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>

root@s1:~ # sysctl hw.em
hw.em.max_interrupt_rate: 8000
hw.em.eee_setting: 1
hw.em.rx_process_limit: 100
hw.em.sbp: 0
hw.em.smart_pwr_down: 0
hw.em.rx_abs_int_delay: 66
hw.em.tx_abs_int_delay: 66
hw.em.rx_int_delay: 0
hw.em.tx_int_delay: 66
hw.em.disable_crc_stripping: 0
root@s1:~ #

Best Regards,
Cheng Cui