L2SS-460: Do NOT use send_hello during a live connection!

devices/clients/opcua_client.py

@@ -86,7 +86,9 @@ class OPCUAConnection(AsyncCommClient):
         ping the client to make sure the connection with the client is still functional.
         """
         try:
-            await self.client.send_hello()
+            # do a cheap call. NOTE: send_hello is not allowed after establishing a connection,
+            # so cannot be used here. see https://reference.opcfoundation.org/v104/Core/docs/Part6/7.1.3/
+            _ = await self.client.get_namespace_array()
         except Exception as e:
             raise IOError("Lost connection to server %s: %s", self._servername(), e)