IB/core: Allow device-specific per-port sysfs files

Add a new parameter to ib_register_device() so that low-level device
drivers can pass in a pointer to a callback function that will be
called for each port that is registered in sysfs.  This allows
low-level device drivers to create files in

    /sys/class/infiniband/<hca>/ports/<N>/

without having to poke through the internals of the RDMA sysfs handling.

There is no need for an unregister function since the kobject
reference will go to zero when ib_unregister_device() is called.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 3905141..4e94e36 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -662,7 +662,7 @@
 	spin_lock_init(&ibdev->sm_lock);
 	mutex_init(&ibdev->cap_mask_mutex);
 
-	if (ib_register_device(&ibdev->ib_dev))
+	if (ib_register_device(&ibdev->ib_dev, NULL))
 		goto err_map;
 
 	if (mlx4_ib_mad_init(ibdev))