Close net.Conn in conn.Close

Close the connection in conn.Close. This ensures the connection isn't
still alive after conn.Close, which would cause issues when
disconnecting and reconnecting quickly to an upstream server.

conn.go

@@ -84,9 +84,10 @@ func (c *conn) Close() error {
 		return fmt.Errorf("connection already closed")
 	}
 
+	err := c.net.Close()
 	c.closed = true
 	close(c.outgoing)
-	return nil
+	return err
 }
 
 func (c *conn) ReadMessage() (*irc.Message, error) {