function mgp_restartServer($connection)
{
    mgp_stopServer($connection);
    mgp_startServer($connection);
}
<?php

require_once "includes/settings.php";
require_once "classes/Login.php";
$login = new Login();
if ($login->isUserLoggedIn() == true) {
    ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Minecraft Game Panel</title>
</head>
<body>
<?php 
    $connection = new Net_SSH2($server_SSH_address);
    $connection->login($server_SSH_username, $server_SSH_password);
    $status = mgp_stopServer($connection);
    echo $status;
    ?>
<br />
<a href="index.php">Go Back</a>
</body>
</html>
<?php 
} else {
    include "views/not_logged_in.php";
}