This is a tricky one.

Consider a kernel that has this code in net/wireless/wext-core.c:

#ifdef CONFIG_CFG80211_WEXT
        if (dev->ieee80211_ptr && dev->ieee80211_ptr->wiphy)
                handlers = dev->ieee80211_ptr->wiphy->wext;
#endif
#ifdef CONFIG_WIRELESS_EXT
        if (dev->wireless_handlers)
                handlers = dev->wireless_handlers;
#endif

If a kernel is compiled without CONFIG_WIRELESS_EXT then
compat-drivers can't do wireless extensions against it.
However, if the kernel is compiled with CONFIG_CFG80211_WEXT
then it will try to get the wext handlers from struct wiphy.

Now, struct wiphy in the base kernel and struct wiphy in
compat-drivers don't match, so the kernel crashes!!

To fix this, add lots of padding to compat-drivers's
struct wiphy so that the "wext" pointer is guaranteed
to be NULL.

Make sure the padding is larger than the struct so we
don't ever run into this again because the wext pointer
moved due to struct enlargements.