net/mlx4_en: Optimize Rx fast path filter checks

Currently, RX path code that does RX filtering is not optimized
and does an expensive conversion. In order to use ether_addr_equal_64bits
which is optimized for such cases, we need the MAC address kept by the device
to be in the form of unsigned char array instead of u64. Store the MAC address
as unsigned char array and convert to/from u64 out of the fast path when needed.
Side effect of this is that we no longer need priv->mac, since it's the same
as dev->dev_addr.

This optimization was suggested by Eric Dumazet <eric.dumazet@gmail.com>

Signed-off-by: Yan Burman <yanb@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>