net: dsa: merge rtnl_lock sections in dsa_slave_create

Currently dsa_slave_create() has two sequences of rtnl_lock/rtnl_unlock
in a row. Remove the rtnl_unlock() and rtnl_lock() in between, such that
the operation can execute slighly faster.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/slave.c

@@ -2022,14 +2022,12 @@ int dsa_slave_create(struct dsa_port *port)
 	}
 
 	rtnl_lock();
+
 	ret = dsa_slave_change_mtu(slave_dev, ETH_DATA_LEN);
-	rtnl_unlock();
 	if (ret && ret != -EOPNOTSUPP)
 		dev_warn(ds->dev, "nonfatal error %d setting MTU to %d on port %d\n",
 			 ret, ETH_DATA_LEN, port->index);
 
-	rtnl_lock();
-
 	ret = register_netdevice(slave_dev);
 	if (ret) {
 		netdev_err(master, "error %d registering interface %s\n",