[nrf fromtree] doc: Documenting value of bt_gatt_attr->perm after bt_gatt_discover()

Permissions can't be discovered so attr->perm is always 0 when returned
from bt_gatt_discover()

Signed-off-by: Pierce Lowe <[email protected]>
Signed-off-by: Herman Berget <[email protected]>
(cherry picked from commit 8800c2b)

Author: Pieloaf

include/zephyr/bluetooth/gatt.h

@@ -172,7 +172,10 @@ struct bt_gatt_attr {
 	void *user_data;
 	/** Attribute handle */
 	uint16_t handle;
-	/** Attribute permissions */
+	/** @brief Attribute permissions.
+	 *
+	 * Will be 0 if returned from bt_gatt_discover().
+	 */
 	uint16_t perm;
 };