net/mlx4: fix UDP RSS related settings

Using RSS which takes into account UDP headers is controlled by
a module param, fix the setting of the HW RSS context to align
with that scheme. So far it was uncoditionally allowing hashing
on the UDP headers.

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