net/sfc: fix main MAC address handling

net/sfc: fix main MAC address handling

There is a school of thought that rte_eth_dev_default_mac_addr_set()
must call the PMD callback first and then save the new MAC address
in dev->data->mac_addrs[0]. If this concept gets approved, it will
break the current approach used in sfc driver as the latter relies
on the assumption that the new MAC address is already contained in
dev->data->mac_addrs[0], and, if adapter restart is needed to make
the HW apply the new address, the outdated value will be retrieved
from dev->data. In order to preclude any possible bugs, this patch
adds device private storage for the up-to-date copy of the address.

Fixes: c100fd464bb7 ("net/sfc: support main MAC address change")
Cc: stable@dpdk.org
Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>