VIMAGE PF fixes #4

[• rodrigc]

Summary

Instead of creating a purge thread for every vnet, create
a single purge thread and clean up all vnets from this thread.

Test Plan

(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

[zec]

sys/netpfil/pf/pf.c

1384

*v could be marked as __unused

sys/netpfil/pf/pf_ioctl.c

282

Passing curvnet as an argument here is redundant now.

[• rodrigc]

Committed in rS276747