net/mlx5_core: Make ipv4/ipv6 location more clear

Change the mlx5 firmware interface header to make it
more clear which bytes should be used by IPv4 or
IPv6 addresses.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>