Macro mqtt_client 

macro_rules! mqtt_client {
    () => { ... };
}

Create a crate::net_mqtt::Client that works in both heap and zero-heap modes. In zero-heap mode the per-connection RX/TX buffers (CONFIG_OVE_NET_MQTT_RX_BUF / CONFIG_OVE_NET_MQTT_TX_BUF) live in the client storage.