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>

drivers/infiniband/hw/ipath/ipath_verbs.c

@@ -2182,7 +2182,7 @@ int ipath_register_ib_device(struct ipath_devdata *dd)
 	snprintf(dev->node_desc, sizeof(dev->node_desc),
 		 IPATH_IDSTR " %s", init_utsname()->nodename);
 
-	ret = ib_register_device(dev);
+	ret = ib_register_device(dev, NULL);
 	if (ret)
 		goto err_reg;