net/mlx4_core: Add support for RoCE v2 entropy

In RoCE v2 we need to choose a source UDP port, we do so by using
entropy over the source and dest QPNs.

Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>