net/mlx5: E-switch: Change eswitch mode only via devlink command

Enable or disable switchdev according to the eswitch mode set by
devlink command. So it is not changed by other functions anymore.

Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>