Bluetooth: hci.h: Avoid a couple -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

struct hci_std_codecs and struct hci_std_codecs_v2 are flexible
structures, this is structures that contain a flexible-array member
(__u8 codec[]; and struct hci_std_codec_v2 codec[];, correspondingly.)

Since struct hci_rp_read_local_supported_codecs and struct
hci_rp_read_local_supported_codecs_v2 are defined by hardware, we
create the new struct hci_std_codecs_hdr and struct hci_std_codecs_v2_hdr
types, and use them to replace the object types causing trouble in
struct hci_rp_read_local_supported_codecs and struct
hci_rp_read_local_supported_codecs_v2, namely struct hci_std_codecs
std_codecs; and struct hci_std_codecs_v2_hdr std_codecs;.

Also, once -fms-extensions is enabled, we can use transparent struct
members in both struct hci_std_codecs and struct hci_std_codecs_v2_hdr.

Notice that the newly created types does not contain the flex-array
member `codec`, which is the object causing the -Wfamnae warnings.

After these changes, the size of struct hci_rp_read_local_supported_codecs
and struct hci_rp_read_local_supported_codecs_v2, along with their
member's offsets remain the same, hence the memory layouts don't
change:

Before changes:
struct hci_rp_read_local_supported_codecs {
        __u8                       status;               /*     0     1 */
        struct hci_std_codecs      std_codecs;           /*     1     1 */
        struct hci_vnd_codecs      vnd_codecs;           /*     2     1 */

        /* size: 3, cachelines: 1, members: 3 */
        /* last cacheline: 3 bytes */
} __attribute__((__packed__));

struct hci_rp_read_local_supported_codecs_v2 {
        __u8                       status;               /*     0     1 */
        struct hci_std_codecs_v2   std_codecs;           /*     1     1 */
        struct hci_vnd_codecs_v2   vendor_codecs;        /*     2     1 */

        /* size: 3, cachelines: 1, members: 3 */
        /* last cacheline: 3 bytes */
} __attribute__((__packed__));

After changes:
struct hci_rp_read_local_supported_codecs {
	__u8                       status;               /*     0     1 */
	struct hci_std_codecs_hdr  std_codecs;           /*     1     1 */
	struct hci_vnd_codecs      vnd_codecs;           /*     2     1 */

	/* size: 3, cachelines: 1, members: 3 */
	/* last cacheline: 3 bytes */
} __attribute__((__packed__));

struct hci_rp_read_local_supported_codecs_v2 {
	__u8                       status;               /*     0     1 */
	struct hci_std_codecs_v2_hdr std_codecs;         /*     1     1 */
	struct hci_vnd_codecs_v2   vendor_codecs;        /*     2     1 */

	/* size: 3, cachelines: 1, members: 3 */
	/* last cacheline: 3 bytes */
} __attribute__((__packed__));

With these changes fix the following warnings:

include/net/bluetooth/hci.h:1490:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
include/net/bluetooth/hci.h:1525:34: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>