Bluetooth: ISO: Use sk_sndtimeo as conn_timeout

This aligns the usage of socket sk_sndtimeo as conn_timeout when
initiating a connection and then use it when scheduling the
resulting HCI command, similar to what has been done in bf98feea
("Bluetooth: hci_conn: Always use sk_timeo as conn_timeout").

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>