devfs.rules: Correctly unhide pf in vnet jails

Revision 9e9be081d8 introduced a new devfs rule devfsrules_jail_vnet. It
includes rule devfsrules_jail which include other rules. Unfortunately
devfs could not recursively parse the action include and thus
devfsrules_jail_vnet will expose all nodes.

PR: 255660
Reviewed by: kp
Obtained from: Gijs Peskens <gijs@peskens.net>
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D32814

(cherry picked from commit 7acd322ebe2072b1d73b1d19c14ab12a300ba8e8)