pf: Introduce DIOCKILLSTATESNV

Introduce an nvlist based alternative to DIOCKILLSTATES.

MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D30054

(cherry picked from commit e989530a09b6e9f77b89c950ecf32f1b4fa709da)