As of 2.6.20, the sysfs_create_file function has a return value and
complains if we ignore the results.  Jeff Garzik sent a patch that
attends to the results:

  Message-ID: <20061004135819.GA29526@havoc.gtf.org>

... but Greg KH had a nicer patch that used the new "group" feature.

  Message-Id: <20061003183705.27E1091A6EB@imap.suse.de>

Greg's patch had a bug that was subsequently fixed by Dennis Stosberg
in

  Message-ID: <20061113081520.G77d5ed8a@leonov.stosberg.net>

... where he added the NULL that was missing from Greg's array.

For conf/12, we use the groups feature if it is present in the kernel
for which we're building the aoe driver.