(1) Boot a kernel with VIMAGE enabled
(2) Create a vnet jail
jail -c persist name=testjail001 vnet path=/ host.hostname=testjail001 allow.raw_sockets allow.socket_af
(3) Start pf inside the jail
service start pf
(4) Delete the vnet jail
jail -r testjail001
Without this patch, the kernel would panic in step (4). With the patch,
the kernel does not panic