net: ethernet: ti: cpsw: fix ASSERT_RTNL() warning during resume

netif_set_real_num_tx/rx_queues() are required to be called with rtnl_lock
taken, otherwise ASSERT_RTNL() warning will be triggered - which happens
now during System resume from suspend:
cpsw_resume()
|- cpsw_ndo_open()
  |- netif_set_real_num_tx/rx_queues()
     |- ASSERT_RTNL();

Hence, fix it by surrounding cpsw_ndo_open() by rtnl_lock/unlock() calls.

Cc: Dave Gerlach <d-gerlach@ti.com>
Cc: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Fixes: commit e05107e ("net: ethernet: ti: cpsw: add multi queue support")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Tested-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ti/cpsw.c

@@ -2930,6 +2930,8 @@ static int cpsw_resume(struct device *dev)
 	/* Select default pin state */
 	pinctrl_pm_select_default_state(dev);
 
+	/* shut up ASSERT_RTNL() warning in netif_set_real_num_tx/rx_queues */
+	rtnl_lock();
 	if (cpsw->data.dual_emac) {
 		int i;
 
@@ -2941,6 +2943,8 @@ static int cpsw_resume(struct device *dev)
 		if (netif_running(ndev))
 			cpsw_ndo_open(ndev);
 	}
+	rtnl_unlock();
+
 	return 0;
 }
 #endif