net/mlx5: Avoid dereferencing uninitialized pointer

In NETDEV_CHANGEUPPER event the upper_info field is valid
only when linking is true. Otherwise it should be ignored.

Fixes: 7907f23a (net/mlx5: Implement RoCE LAG feature)
Signed-off-by: Talat Batheesh <talatb@mellanox.com>
Reviewed-by: Aviv Heller <avivh@mellanox.com>
Reviewed-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/lag.c

@@ -294,7 +294,7 @@ static int mlx5_handle_changeupper_event(struct mlx5_lag *ldev,
 					 struct netdev_notifier_changeupper_info *info)
 {
 	struct net_device *upper = info->upper_dev, *ndev_tmp;
-	struct netdev_lag_upper_info *lag_upper_info;
+	struct netdev_lag_upper_info *lag_upper_info = NULL;
 	bool is_bonded;
 	int bond_status = 0;
 	int num_slaves = 0;
@@ -303,6 +303,7 @@ static int mlx5_handle_changeupper_event(struct mlx5_lag *ldev,
 	if (!netif_is_lag_master(upper))
 		return 0;
 
+	if (info->linking)
 		lag_upper_info = info->upper_info;
 
 	/* The event may still be of interest if the slave does not belong to