pf: revert: Use counter(9) for pf_state byte/packet tracking

stats are not shared and consequently per-CPU counters only waste
memory.

No slowdown was measured when passing over 20M pps.

Reviewed by: kp
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 55cc305dfcad0ad7c4f528fa47f7473927e8223a)