sysutils/lsof and defining _KERNEL

[Lowell Gilbert]

I'm having trouble building lsof, because it's defining _KERNEL to pull
in ZFS structures, and then tries to find opt_kdtrace.h, which isn't
really relevant. I suspect I've messed up something in my system
somehow, but I've been banging my head against this for hours over the
last few days, and I can't figure out what's going on.

Any clues?