net: wwan: iosm: Convert single instance struct member to flexible array

struct mux_adth actually ends with multiple struct mux_adth_dg members.
This is seen both in the comments about the member:

/**
* struct mux_adth - Structure of the Aggregated Datagram Table Header.
...
* @dg: datagramm table with variable length
*/

and in the preparation for populating it:

adth_dg_size = offsetof(struct mux_adth, dg) +
ul_adb->dg_count[i] * sizeof(*dg);
...
adth_dg_size -= offsetof(struct mux_adth, dg);
memcpy(&adth->dg, ul_adb->dg[i], adth_dg_size);

This was reported as a run-time false positive warning:

memcpy: detected field-spanning write (size 16) of single field "&adth->dg" at drivers/net/wwan/iosm/iosm_ipc_mux_codec.c:852 (size 8)

Adjust the struct mux_adth definition and associated sizeof() math; no binary
output differences are observed in the resulting object file.

Reported-by: Florian Klink <[e-mail]>
Closes: https://lore.kernel.org/lkml/[e-mail]/
Fixes: 1f52d7b62285 ("net: wwan: iosm: Enable M.2 7360 WWAN card support")
Cc: M Chetan Kumar <[e-mail]>
Cc: Bagas Sanjaya <[e-mail]>
Cc: Intel Corporation <[e-mail]>
Cc: Loic Poulain <[e-mail]>
Cc: Sergey Ryazanov <[e-mail]>
Cc: Johannes Berg <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Cc: Jakub Kicinski <[e-mail]>
Cc: Paolo Abeni <[e-mail]>
Cc: "Gustavo A. R. Silva" <[e-mail]>
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: Gustavo A. R. Silva <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/net/wwan/iosm/iosm_ipc_mux_codec.c

···
 		if (adth->signature != cpu_to_le32(IOSM_AGGR_MUX_SIG_ADTH))
 			goto adb_decode_err;
 
-		if (le16_to_cpu(adth->table_length) < (sizeof(struct mux_adth) -
-				sizeof(struct mux_adth_dg)))
+		if (le16_to_cpu(adth->table_length) < sizeof(struct mux_adth))
 			goto adb_decode_err;
 
 		/* Calculate the number of datagrams. */
 		nr_of_dg = (le16_to_cpu(adth->table_length) -
-					sizeof(struct mux_adth) +
-					sizeof(struct mux_adth_dg)) /
+					sizeof(struct mux_adth)) /
 					sizeof(struct mux_adth_dg);
 
 		/* Is the datagram table empty ? */
···
 		}
 
 		/* New aggregated datagram table. */
-		dg = &adth->dg;
+		dg = adth->dg;
 		if (mux_dl_process_dg(ipc_mux, adbh, dg, skb, if_id,
 				      nr_of_dg) < 0)
 			goto adb_decode_err;
···
 			adth->if_id = i;
 			adth->table_length = cpu_to_le16(adth_dg_size);
 			adth_dg_size -= offsetof(struct mux_adth, dg);
-			memcpy(&adth->dg, ul_adb->dg[i], adth_dg_size);
+			memcpy(adth->dg, ul_adb->dg[i], adth_dg_size);
 			ul_adb->if_cnt++;
 		}
 
···
 
 		if (adth->signature == cpu_to_le32(IOSM_AGGR_MUX_SIG_ADTH)) {
 			nr_of_dg = (le16_to_cpu(adth->table_length) -
-					sizeof(struct mux_adth) +
-					sizeof(struct mux_adth_dg)) /
+					sizeof(struct mux_adth)) /
 					sizeof(struct mux_adth_dg);
 
 			if (nr_of_dg <= 0)
 				return payload_size;
 
-			dg = &adth->dg;
+			dg = adth->dg;
 
 			for (i = 0; i < nr_of_dg; i++, dg++) {
 				if (le32_to_cpu(dg->datagram_index) <

drivers/net/wwan/iosm/iosm_ipc_mux_codec.h

···
 	u8 opt_ipv4v6;
 	__le32 next_table_index;
 	__le32 reserved2;
-	struct mux_adth_dg dg;
+	struct mux_adth_dg dg[];
 };
 
 /**