* solve modbus issue #33872
CONF_DELAY was used in a serial connection, which is not
permitted.
Sometimes async_update is called after async_setup is completed,
but before event EVENT_HOMEASSISTANT_START is issued, leading to
a missing object.
* resolve review comment.
Do not wait for start event, but activate pymodbus directly in
async setup.
* review 2
Remark, this does not work, async_setup hangs.
clean start_modbus() from async calls, leaving only the pymodbus
setup.
* review 2a
Moved listen_once back to start_modbus, since it is sync.
b2083a7bee