Kernel panic with if_sf.ko

Hello there,

I've started to observe the following rather annoying panic if I boot
with if_sf loaded (via loader.conf) and having sf0 configured via DHCP
on recent -CURRENT.  If I comment out driver from loader.conf and load
it manually (via kldload(8)) after system boots, it loads and gets
configured just fine.

Any clues here?  Attached is relevant dmesg + DDB trace (debug kernel
with WITNESS).  I'm happy to provide any additional information (that
is, ps/show uma/malloc, whatever).

Thanks.

./danfe