net/mlx5e: Refactor mlx5e_eswitch_{*}rep() helpers

Change the helper to functions to accept constant pointer to struct
net_device. This is necessary for following patches in series that pass
mlx5e_eswitch_rep() as a callback to kernel bridge infrastructure code.

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Reviewed-by: Jianbo Liu <jianbol@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>