drivers: bluetooth: add more documentation for BT_HCI_SET_PUBLIC_ADDR

Hopefully this should now aid driver developers as well as application
developers.

(cherry picked from commit b8856ae)

Original-Signed-off-by: Armin Brauns <armin.brauns@embedded-solutions.at>
GitOrigin-RevId: b8856ae
Change-Id: Ic14a362d9800b03061236061a8f0056a02df2b02
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5095324
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Commit-Queue: Fabio Baltieri <fabiobaltieri@google.com>
Tested-by: Fabio Baltieri <fabiobaltieri@google.com>
Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>

drivers/bluetooth/hci/Kconfig

@@ -175,6 +175,9 @@ config BT_HCI_SET_PUBLIC_ADDR
 	  public identity through vendor-specific commands. They can then implement the
 	  setup() HCI driver API function and get the address to set from the public_addr field.
 
+	  From the application side, the public address is set using the first call to
+	  bt_id_create(), before calling bt_enable().
+
 config BT_HCI_SETUP
 	bool
 	help