Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add a DFS debugging mode which is useful when doing automated DFS
compliance testing.

In order to allow for radar pattern matching to occur, the DFS CAC/NOL
handling needs to be made configurable. This commit introduces a new
sysctl, "net.wlan.dfs_debug", which controls which DFS debug mode
net80211 is in.

* 0 = default, CSA/NOL handling as per normal.
* 1 = announce a CSA, but don't add the channel to the non-occupy list
(NOL.)
* 2 = disable both CSA and NOL - only print that a radar event occured.

This code is not compiled/enabled by default as it breaks regulatory
handling. A user must enable IEEE80211_DFS_DEBUG in their kernel
configuration file for this option to become available.

Obtained from: Atheros

Fix definition of IEEE80211_CHAN_MAX; it was defined as 255 but
really was meant to be 256. Adjust usage accordingly and replace
bogus usage of this value in checking IEEE channel #'s.

NB: this causes an ABI change; ifconfig must be recompiled

Multi-bss (aka vap) support for 802.11 devices.

Note this includes changes to all drivers and moves some device firmware
loading to use firmware(9) and a separate module (e.g. ral). Also there
no longer are separate wlan_scan* modules; this functionality is now
bundled into the wlan module.

Supported by: Hobnob and Marvell
Reviewed by: many
Obtained from: Atheros (some bits)