mlx4_en: reconfiguring mac address.

When Mac address is removed from one port of the CX2 device, the other device
should reconfigure its Mac.
This fixes an issue with failover, when both ports have the same Mac address,
and one of the ports, is closed, the second one stops receiving traffic.
(bugzilla #1965 at bugs.openfabrics.org)

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>