dtrace probe not listed

[Farhan Khan]

I do not see the function ifhwioctl listed when I run dtrace -l. This function is located in /usr/src/sys/net/if.c.
I thought maybe this was optimized out, so I set the following in my /etc/make.conf

CFLAGS= -O0 -fno-inline

But it is still not listed.

What may be causing this lack of probe?