IB/mlx5: Enable "block multicast loopback" for kernel consumers

In commit f360d88a2e, we advertise blocking multicast loopback to both
kernel and userspace consumers, but don't allow kernel consumers (e.g IPoIB)
to use it with their UD QPs.  Fix that.

Fixes: f360d88a2e ("IB/mlx5: Add block multicast loopback support")
Reported-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/mlx5/qp.c

@@ -675,7 +675,7 @@ static int create_kernel_qp(struct mlx5_ib_dev *dev,
 	int err;
 
 	uuari = &dev->mdev.priv.uuari;
-	if (init_attr->create_flags & ~IB_QP_CREATE_SIGNATURE_EN)
+	if (init_attr->create_flags & ~(IB_QP_CREATE_SIGNATURE_EN | IB_QP_CREATE_BLOCK_MULTICAST_LOOPBACK))
 		return -EINVAL;
 
 	if (init_attr->qp_type == MLX5_IB_QPT_REG_UMR)