DFS: Remove the os_random() fallback

Remove the fallback dependency on os_random() from the code that gets a
valid DFS channel. This is exceptionally unlikely to ever be called as
the call to os_get_random() is unlikely to fail. The intention is to
facilitate future removal of os_random() as it uses a low quality PRNG.

Signed-off-by: Nick Lowe <nick.lowe@lugatech.com>

src/ap/dfs.c

@@ -450,7 +450,7 @@ dfs_get_valid_channel(struct hostapd_iface *iface,
 		return NULL;
 
 	if (os_get_random((u8 *) &_rand, sizeof(_rand)) < 0)
-		_rand = os_random();
+		return NULL;
 	chan_idx = _rand % num_available_chandefs;
 	dfs_find_channel(iface, &chan, chan_idx, skip_radar);