hostapd: Add AP DFS support

hostapd: Add AP DFS support

Add DFS structures/events handlers, CAC handling, and radar detection.
By default, after radar is detected or the channel became unavailable, a
random channel will be chosen.

This patches are based on the original work by Boris Presman and
Victor Goldenshtein. Most of the DFS code is moved to a new dfs.c/dfs.h
files.

Cc: Boris Presman <boris.presman@ti.com>
Cc: Victor Goldenshtein <victorg@ti.com>
Signed-hostap: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-hostap: Janusz Dziedzic <janusz.dziedzic@tieto.com>