add conn_idle_timeout for server

[silence-coding]

Should we add idle timeout for the server? Without idle timeout, the service cannot quickly release idle connections. In this case, the client can set up a large number of idle connections with the hyper server, exhausting the hyper resources.

[CodesInChaos]

Even if the server implements idle timeouts, an attacker can simply send the data very slowly (slowloris attack).

[silence-coding]

Although this capability cannot solve slow attacks, when the connection is idle for a long time, it is necessary for the hyper server to close the connection.