net/mlx4: Add RSS support for fragmented IP datagrams

Enable RSS support for fragmented IP packets, when device supports it.
Until now, fragmented IP packets were directed only to the default_qpn.
Since IP fragments (datagram) have no upper protocols (L3 IP packets),
hash is performed on 3-tuple - dst MAC, source IP and dest IP. The HW
makes sure that this holds for the 1st fragment too, so all fragments
go to the same QP.

Signed-off-by: Ido Shamay <idos@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>