pfctl: Stop sharing pf_ruleset.c with the kernel

Now that we've split up the datastructures used by the kernel and
userspace there's essentually no more overlap between the pf_ruleset.c
code used by userspace and kernelspace.

Copy the userspace bits to the pfctl directory and stop using the kernel
file.

Reviewed by: philip
MFC after: 2 weeks
Sponsored by: Orange Business Services
Differential Revision: https://reviews.freebsd.org/D27764