ipw2x00: Avoid field-overflowing memcpy()

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

libipw_read_qos_param_element() copies a struct libipw_info_element
into a struct libipw_qos_information_element, but is actually wanting to
copy into the larger struct libipw_qos_parameter_info (the contents of
ac_params_record[] is later examined). Refactor the routine to perform
centralized checks, and copy the entire contents directly (since the id
and len members match the elementID and length members):

struct libipw_info_element {
        u8 id;
        u8 len;
        u8 data[];
} __packed;

struct libipw_qos_information_element {
        u8 elementID;
        u8 length;
        u8 qui[QOS_OUI_LEN];
        u8 qui_type;
        u8 qui_subtype;
        u8 version;
        u8 ac_info;
} __packed;

struct libipw_qos_parameter_info {
        struct libipw_qos_information_element info_element;
        u8 reserved;
        struct libipw_qos_ac_parameter ac_params_record[QOS_QUEUE_NUM];
} __packed;

Cc: Stanislav Yakovlev <stas.yakovlev@gmail.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210819202825.3545692-2-keescook@chromium.org