net/mlx4: move RSS related definitions to be global

Towards adding RSS support for IB drivers/application who use
the mlx4 HW, make the RSS related definitions global and change
the mlx4_en driver to use them.

Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>