net/mlx5: Lag, use actual number of lag ports

Refactor the entire lag code to use ldev->ports instead of hard-coded
defines (like MLX5_MAX_PORTS) for its operations.

Signed-off-by: Mark Bloch <mbloch@nvidia.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>