net/mlx5e: Refactor mlx5e_netdev_init/cleanup to mlx5e_priv_init/cleanup

We actually initialize priv and not netdev. The only call to
set netdev carrier will be moved in the following commit.

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