net/mlx5: LAG, block multipath LAG in case ldev have more than 2 ports

multipath LAG is not supported over more than two ports. Add a check in
order to block multipath LAG over such configurations.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>