mlx4: use netdev_rss_key_fill() helper

Use of well known RSS key increases attack surface.
Switch to a random one, using generic helper so that all
ports share a common key.

Also provide ethtool -x support to fetch RSS key

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
Simple merge

diff --cc drivers/net/ethernet/mellanox/mlx4/en_rx.c
Simple merge

diff --cc include/linux/mlx4/qp.h
Simple merge