drivers/net: do not use private ethdev data

drivers/net: do not use private ethdev data

We introduced private rte_eth_dev_data to allow vdev to be created
both in primary process and secondary process(es). This is not
friendly to multi-process model, for example, it leads to port id
contention issue if two processes both find the data entry is free.

And to get stats of primary vdev in secondary, we must allocate
from the pre-defined array so that we can find it.

Suggested-by: Bruce Richardson <bruce.richardson@intel.com>
Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Reviewed-by: Qi Zhang <qi.z.zhang@intel.com>