ipfilter Ansification: Convert K&R function declarations to ANSI

[cy]

Summary

Convert ipfilter kernel 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).

Test Plan

Currently running here.

[cy]

A copy can be found on github (https://github.com/cschuber/freebsd-ipf-ansi).

[glebius]

The uppercase INLINE, which I guess is a macro, can be substituted to lowercase inline, which is part of modern C in the same sweep.

P.S. IMHO such mechanical sweeps don't deserve a publication of review and don't require reviewers.

[cy]

Thanks. INLINE --> inline should be a separate pair of commits.

Also planned is conform "return" statements to style(9).