When submitting HCI_OP_LE_CREATE_CIS the code shall wait for
HCI_EVT_LE_CIS_ESTABLISHED thus enforcing the serialization of
HCI_OP_LE_CREATE_CIS as the Core spec does not allow to send them in
parallel:

  BLUETOOTH CORE SPECIFICATION Version 5.3 | Vol 4, Part E page 2566:

  If the Host issues this command before all the HCI_LE_CIS_Established
  events from the previous use of the command have been generated, the
  Controller shall return the error code Command Disallowed (0x0C).
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>