ethdev: change device info get callback to return int

ethdev: change device info get callback to return int

Change eth_dev_infos_get_t return value from void to int.
Make eth_dev_infos_get_t implementations across all drivers to return
negative errno values if case of error conditions.

Signed-off-by: Ivan Ilchenko <ivan.ilchenko@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>