connection_keepalive sends pings even if client is idle

With the default configuration of connection_timeout=0s and connection_keepalive=300s, a client that connects to MaxScale and then goes idle is never timed out. This happens because connection_keepalive sends the keepalive pings regardless of the client state. This was not the intended purpose of the feature and it should only send the keepalive pings if the client connection has been idle for less than the configured connection_keepalive value. If the connection goes idle for longer than that, the keepalive pings should stop.