mlx4_core: Adjust flow steering attach wrapper so that IB works on SR-IOV VFs

Currently, the InfiniBand stack does not support flow steering at the
verbs level -- the only usage of flow steering in the IB driver is for
L2 multicast attaches.  We need to add the IB case to procedure
mlx4_QP_FLOW_STEERING_ATTACH_wrapper() to allow IPoIB to work on VFs
on ConnectX-3 when flow steering is enabled.

Currently, the IB case in mlx4_QP_FLOW_STEERING_ATTACH_wrapper() is missing,
so the procedure returns -EINVAL and IPoIB on VFs breaks.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>