mlx4_en: FIX: Setting default_qpn before using it

When UDP RSS is enabled, we use same QPN for TCP and UDP ranges
The bug is that the default_qpn was used base UDP qpn before it
was set.
Fixes bug introduced in commit: 1202d460

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>