ipflter: ANSIfy userland function declarations
Convert ipfilter userland function declarations from K&R to ANSI. This
syncs our function declarations with NetBSD hg commit 75edcd7552a0
(apply our changes). Though not copied from NetBSD, this change was
partially inspired by NetBSD's work and inspired by style(9).
Reviewed by: glebius (for network)
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D33595