core: propagate service state to socket in more load states

It makes sense to filter state changes for some load states that
shouldn't happen, but the common cases should be accepted, because they
might happen during runtime when "systemctl daemon-reload" is issued and
unit files changed state in between. Otherwise we lose events.

Fixes: #4708

src/core/socket.c

@@ -3257,7 +3257,12 @@ static void socket_trigger_notify(Unit *u, Unit *other) {
         assert(other);
 
         /* Filter out invocations with bogus state */
-        if (other->load_state != UNIT_LOADED || other->type != UNIT_SERVICE)
+        if (!IN_SET(other->load_state,
+                    UNIT_LOADED,
+                    UNIT_NOT_FOUND,
+                    UNIT_BAD_SETTING,
+                    UNIT_ERROR,
+                    UNIT_MASKED) || other->type != UNIT_SERVICE)
                 return;
 
         /* Don't propagate state changes from the service if we are already down */