alx: take rtnl before calling __alx_open from resume

The __alx_open function can be called from ndo_open, which is called
under RTNL, or from alx_resume, which isn't. Since commit d768319cd427,
we're calling the netif_set_real_num_{tx,rx}_queues functions, which
need to be called under RTNL.

This is similar to commit 0c2cc02e571a ("igb: Move the calls to set the
Tx and Rx queues into igb_open").

Fixes: d768319cd427 ("alx: enable multiple tx queues")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/alx/main.c

@@ -1897,13 +1897,19 @@ static int alx_resume(struct device *dev)
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct alx_priv *alx = pci_get_drvdata(pdev);
 	struct alx_hw *hw = &alx->hw;
+	int err;
 
 	alx_reset_phy(hw);
 
 	if (!netif_running(alx->dev))
 		return 0;
 	netif_device_attach(alx->dev);
-	return __alx_open(alx, true);
+
+	rtnl_lock();
+	err = __alx_open(alx, true);
+	rtnl_unlock();
+
+	return err;
 }
 
 static SIMPLE_DEV_PM_OPS(alx_pm_ops, alx_suspend, alx_resume);