net/mlx5e: Replace usage of mlx5e_devlink_get_dl_port() by netdev->devlink_port

net/mlx5e: Replace usage of mlx5e_devlink_get_dl_port() by netdev->devlink_port

On places where netdev pointer is available, access related devlink_port
pointer by netdev->devlink_port instead of using
mlx5e_devlink_get_dl_port() which is going to be removed.

Move SET_NETDEV_DEVLINK_PORT() call right after devlink port
registration to make sure netdev->devlink_port is valid.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>