Crash with ZFS between r296491 and r296548

Hi!

I use Root on ZFS and my laptop doesn't boot with a kernel from r296548
and world from r296491 (so older than kernel). Ed hits a similar crash.

Here are the dmesg and backtrace of zfs(8):
https://gist.github.com/dumbbell/c9978ad4ac70214f0f47

With a kernel and world from r296491, everything is ok.

I didn't have the time to bisect the bad commit yet, so this is mostly a
warning for other. Maybe someone will know what's wrong :)

-- 
Jean-Sébastien Pédron