staging: wlan-ng: Remove pointless a3/a4 union

staging: wlan-ng: Remove pointless a3/a4 union

There is no need for the a3/a4 union. The two structs are identical
except for the addition of a4. Excepting one place, the structs are
only ever used in the union, and the union is always allocated at full
size. The one instance of the a3-specific struct can be replaced with
the full version, as no sizing information is used. Replace the union
with the a4 version of the struct. "diffoscope" reports there are no
object code differences after this change.

Cc: Allen Pais <apais@linux.microsoft.com>
Cc: Romain Perier <romain.perier@gmail.com>
Cc: Chen Lin <chen.lin5@zte.com.cn>
Cc: Ivan Safonov <insafonov@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-staging@lists.linux.dev
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210819174537.3499227-2-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>