add dkms dependency in Red Hat unit file

add dkms dependency in Red Hat unit file

Currently, there is no explicit relationship between OpenAFS and dkms.
If dkms needs to rebuild the kernel module, OpenAFS will fail to mount
because modprobe will not load the module.  This change specifies that
OpenAFS should run after dkms if dkms is present.

Reviewed-on: https://gerrit.openafs.org/13654
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Laß <lass@mail.uni-paderborn.de>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit fbe2a03aa69bc19768302685d902a25e4d6e157a)

Change-Id: If08df50128a29642e9cdfc311811b99a7889a158
Reviewed-on: https://gerrit.openafs.org/13674
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: khm <khm@sciops.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>