RDMA/mlx4: Discard unknown SQP work requests

There is no need to crash the machine if unknown work request was
received in SQP MAD.

Cc: <stable@vger.kernel.org> # 3.6
Fixes: 37bfc7c1 ("IB/mlx4: SR-IOV multiplex and demultiplex MADs")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>