Two different set_mac functions exists but stmmac_dwmac4_set_mac() is
only used for enabling and never for disabling.
So on dwmac4, the MAC RX/TX is never disabled.
This patch add a generic function pointer set_mac() to stmmac_ops and
replace all call to stmmac_set_mac/stmmac_dwmac4_set_mac by a c
From: Corentin Labbe
Date: Wed, 22 Mar 2017 14:29:04 +0100
> @@ -2224,7 +,8 @@ static int stmmac_release(struct net_device *dev)
> free_dma_desc_resources(priv);
>
> /* Disable the MAC Rx/Tx */
> - stmmac_set_mac(priv->ioaddr, false);
> + if (priv->hw->mac->set_mac)
> +
