Switch if_run.c to use a bitmap for debug levels rather than arbitrary
values. This more closely matches other wifi drivers in the tree.
The bitmap levels have been based closely on other drivers (primarily
[u]rtwn(4)) in the hope that one day these can be unified into a shared
wifi-debug framework.

This is the first step of several pieces of work I'm planning on doing
with the run(4) driver. I may well adjust and refine some of the debug
bitmaps at a later date.

Reviewed by: adrian, avos
Differential Revision: https://reviews.freebsd.org/D8704