IB/mlx5: Fix scatter to CQE in DCT QP creation

When scatter to CQE is enabled on a DCT QP it corrupts the mailbox command
since it tried to treat it as as QP create mailbox command instead of a
DCT create command.

The corrupted mailbox command causes userspace to malfunction as the
device doesn't create the QP as expected.

A new mlx5 capability is exposed to user-space which ensures that it will
not enable the feature on DCT without this fix in the kernel.

Fixes: 5d6ff1babe ("IB/mlx5: Support scatter to CQE for DC transport type")
Signed-off-by: Guy Levi <guyle@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/main.c

@@ -1119,6 +1119,8 @@ static int mlx5_ib_query_device(struct ib_device *ibdev,
 		if (MLX5_CAP_GEN(mdev, qp_packet_based))
 			resp.flags |=
 				MLX5_IB_QUERY_DEV_RESP_PACKET_BASED_CREDIT_MODE;
+
+		resp.flags |= MLX5_IB_QUERY_DEV_RESP_FLAGS_SCAT2CQE_DCT;
 	}
 
 	if (field_avail(typeof(resp), sw_parsing_caps,