net/mlx5: Lag, move E-Switch prerequisite check into lag code

There is no need to expose E-Switch function for something that can be
checked with already present API inside lag code.

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