Only reflect unavailable state in DSMR when disconnected (#84862)

* Only reflect unavailable state in DSMR when disonnected

* Addressreview comment

tests/components/dsmr/test_sensor.py

@@ -24,6 +24,7 @@ from homeassistant.const import (
     ATTR_UNIT_OF_MEASUREMENT,
     ENERGY_KILO_WATT_HOUR,
     STATE_UNAVAILABLE,
+    STATE_UNKNOWN,
     VOLUME_CUBIC_METERS,
     UnitOfPower,
 )
@@ -783,6 +784,10 @@ async def test_reconnect(hass, dsmr_connection_fixture):
 
     assert connection_factory.call_count == 1
 
+    state = hass.states.get("sensor.electricity_meter_power_consumption")
+    assert state
+    assert state.state == STATE_UNKNOWN
+
     # indicate disconnect, release wait lock and allow reconnect to happen
     closed.set()
     # wait for lock set to resolve