pf: Set the pfik_group for userspace
Userspace relies on this pointer to work out if the kif is a group or
not. It can't use it for anything else, because it's a pointer to a
kernel address. Substitute 0xfeedc0de for 'true', so that we don't leak
kernel memory addresses to userspace.
(cherry picked from commit d69cc040147284c414dfd1c9f498dcc7c8291a8b)