docs: mention sys default if 0

Author: pH14

tokio-postgres/src/config.rs

@@ -98,7 +98,7 @@ pub enum Host {
 ///     can resolve to multiple IP addresses, and this limit is applied to each address. Defaults to no timeout.
 /// * `tcp_user_timeout` - The time limit that transmitted data may remain unacknowledged before a connection is forcibly closed.
 ///     This is ignored for Unix domain socket connections. It is only supported on systems where TCP_USER_TIMEOUT is available
-///     and will default to the system default; on other systems, it has no effect.
+///     and will default to the system default if omitted or set to 0; on other systems, it has no effect.
 /// * `keepalives` - Controls the use of TCP keepalive. A value of 0 disables keepalive and nonzero integers enable it.
 ///     This option is ignored when connecting with Unix sockets. Defaults to on.
 /// * `keepalives_idle` - The number of seconds of inactivity after which a keepalive message is sent to the server.
@@ -348,8 +348,8 @@ impl Config {
     /// Sets the TCP user timeout.
     ///
     /// This is ignored for Unix domain socket connections. It is only supported on systems where
-    /// TCP_USER_TIMEOUT is available and will default to the system default; on other systems,
-    /// it has no effect.
+    /// TCP_USER_TIMEOUT is available and will default to the system default if omitted or set to 0;
+    /// on other systems, it has no effect.
     pub fn tcp_user_timeout(&mut self, tcp_user_timeout: Duration) -> &mut Config {
         self.tcp_user_timeout = Some(tcp_user_timeout);
         self