[nrf fromtree] Bluetooth: Host: Specify parameter needs of bt_set_name

State that the name given to `bt_set_name` must be null terminated.

If not, the behavior of the function may be wrong as it's using `strlen`
to get the length of the given name and `strcmp` to compare it to the
current device name. Both of those functions expect null terminated string.

Signed-off-by: Théo Battrel <[email protected]>
(cherry picked from commit 7884b92)

Author: theob-pro

include/zephyr/bluetooth/bluetooth.h

@@ -268,7 +268,7 @@ bool bt_is_ready(void);
  *
  * @sa @kconfig{CONFIG_BT_DEVICE_NAME_MAX}.
  *
- * @param name New name
+ * @param name New name, must be null terminated
  *
  * @return Zero on success or (negative) error code otherwise.
  */