ipw2x00: potential buffer overflow in libipw_wx_set_encodeext()

The "ext->key_len" is a u16 that comes from the user.  If it's over
SCM_KEY_LEN (32) that could lead to memory corruption.

Fixes: e0d369d1 ("[PATCH] ieee82011: Added WE-18 support to default wireless extension handler")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Stanislav Yakovlev <stas.yakovlev@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/YHaoA1i+8uT4ir4h@mwanda