wifi: cfg80211: Avoid clashing function prototypes

When built with Control Flow Integrity, function prototypes between
caller and function declaration must match. These mismatches are visible
at compile time with the new -Wcast-function-type-strict in Clang[1].

Fix a total of 73 warnings like these:

drivers/net/wireless/intersil/orinoco/wext.c:1379:27: warning: cast from 'int (*)(struct net_device *, struct iw_request_info *, struct iw_param *, char *)' to 'iw_handler' (aka 'int (*)(struct net_device *, struct iw_request_info *, union iwreq_data *, char *)') converts to incompatible function type [-Wcast-function-type-strict]
IW_HANDLER(SIOCGIWPOWER, (iw_handler)orinoco_ioctl_getpower),
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

../net/wireless/wext-compat.c:1607:33: warning: cast from 'int (*)(struct net_device *, struct iw_request_info *, struct iw_point *, char *)' to 'iw_handler' (aka 'int (*)(struct net_device *, struct iw_request_info *, union iwreq_data *, char *)') converts to incompatible function type [-Wcast-function-type-strict]
[IW_IOCTL_IDX(SIOCSIWGENIE)] = (iw_handler) cfg80211_wext_siwgenie,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

../drivers/net/wireless/intersil/orinoco/wext.c:1390:27: error: incompatible function pointer types initializing 'const iw_handler' (aka 'int (*const)(struct net_device *, struct iw_request_info *, union iwreq_data *, char *)') with an expression of type 'int (struct net_device *, struct iw_request_info *, struct iw_param *, char *)' [-Wincompatible-function-pointer-types]
IW_HANDLER(SIOCGIWRETRY, cfg80211_wext_giwretry),
^~~~~~~~~~~~~~~~~~~~~~

The cfg80211 Wireless Extension handler callbacks (iw_handler) use a
union for the data argument. Actually use the union and perform explicit
member selection in the function body instead of having a function
prototype mismatch. There are no resulting binary differences
before/after changes.

These changes were made partly manually and partly with the help of
Coccinelle.

Link: https://github.com/KSPP/linux/issues/234
Link: https://reviews.llvm.org/D134831 [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/a68822bf8dd587988131bb6a295280cb4293f05d.1667934775.git.gustavoars@kernel.org

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500

Based on 2 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation #

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 4122 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

cfg80211: remove unused wext handler exports

A lot of code is dedicated to giving drivers the
ability to use cfg80211's wext handlers without
completely converting. However, only orinoco is
currently using this, and it is only partially
using it.

We reduce the size of both the source and binary
by removing those that nobody needs. If a driver
shows up that needs it during conversion, we can
add back those that are needed.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

cfg80211: split wext compatibility to separate header

A lot of drivers erroneously use wext constants
and don't notice since cfg80211.h includes them.
Make this more split up so drivers needing wext
compatibility from cfg80211 need to explicitly
include that from cfg80211-wext.h.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>