IB/mlx4: Add Scatter FCS support over WQ creation

As a default, for Ethernet packets, the device scatters only the payload
of ingress packets. The scatter FCS feature lets the user to get the FCS
(Ethernet's frame check sequence) in the received WR's buffer as a 4
Bytes trailer following the packet's payload.

Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Guy Levi <guyle@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>