RDMA/mlx4: Read pkey table length instead of hardcoded value

If the pkey_table is not available (which is the case when RoCE is not
supported), the cited commit caused a regression where mlx4_devices
without RoCE are not created.

Fix this by returning a pkey table length of zero in procedure
eth_link_query_port() if the pkey-table length reported by the device is
zero.

Link: https://lore.kernel.org/r/20200824110229.1094376-1-leon@kernel.org
Cc: <stable@vger.kernel.org>
Fixes: 1901b91 ("IB/core: Fix potential NULL pointer dereference in pkey cache")
Fixes: fa417f7 ("IB/mlx4: Add support for IBoE")
Signed-off-by: Mark Bloch <markb@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/mlx4/main.c

@@ -784,7 +784,8 @@ static int eth_link_query_port(struct ib_device *ibdev, u8 port,
 	props->ip_gids = true;
 	props->gid_tbl_len	= mdev->dev->caps.gid_table_len[port];
 	props->max_msg_sz	= mdev->dev->caps.max_msg_sz;
-	props->pkey_tbl_len	= 1;
+	if (mdev->dev->caps.pkey_table_len[port])
+		props->pkey_tbl_len = 1;
 	props->max_mtu		= IB_MTU_4096;
 	props->max_vl_num	= 2;
 	props->state		= IB_PORT_DOWN;