Multiple network interfaces and ipv6 ifdisabled set by default

I am running CORE 13 with 4 network interfaces.
Interface1 set to ipv6 autoconfigure. It works fine.
Interface 2 3 4 are marked with ifdisabled by default.
I have to manually set accept_rtadv auto_linklocal -ifdisabled after every reboot for these interfaces.
I have tried Tunables rc.conf. I added Variable: ifconfig_igc3_ipv6 Value: inet6 accept_rtadv auto_linklocal -ifdisabled Type:RC. But it does not work. I don’t see any change in rc.conf and after reboot I have to manually configure interfaces again.

Any suggest?

I found my Tunables landed in /etc/rc.conf.freenas.
It reads – ifconfig_igc3_ipv6=“inet6 accept_rtadv auto_linklocal -ifdisabled”

But it does not work. I still need to activate manually after every reboot.