ethdev: change MAC address get function to return int

ethdev: change MAC address get function to return int

Change rte_eth_macaddr_get() return value from void to int
and return negative errno values in case of error conditions.

Signed-off-by: Igor Romanov <igor.romanov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>