net/mlx4_en: Fix race when setting the device MAC address

Remove unnecessary use of workqueue for the device MAC address setting
flow, and fix a race when setting MAC address which was introduced by
commit c07cb4b0a "net/mlx4_en: Manage hash of MAC addresses per port"

The race happened when mlx4_en_replace_mac was being executed in parallel
with a successive call to ndo_set_mac_address, e.g witn an A/B/A MAC
setting configuration test, the third set fails.

With this change we also properly report an error if set MAC fails.

Signed-off-by: Yan Burman <yanb@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>