net: stmmac: Implement ethtool::nway_reset

Utilize the generic phy_ethtool_nway_reset() helper function to
implement an autonegotiation restart.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac_ethtool.c

@@ -870,6 +870,7 @@ static const struct ethtool_ops stmmac_ethtool_ops = {
 	.get_regs = stmmac_ethtool_gregs,
 	.get_regs_len = stmmac_ethtool_get_regs_len,
 	.get_link = ethtool_op_get_link,
+	.nway_reset = phy_ethtool_nway_reset,
 	.get_pauseparam = stmmac_get_pauseparam,
 	.set_pauseparam = stmmac_set_pauseparam,
 	.get_ethtool_stats = stmmac_get_ethtool_stats,