[DLM] Kconfig: don't show an empty DLM menu

Don't show an empty "Distributed Lock Manager" menu if IP_SCTP=n.

Reported by Dmytro Bagrii in kernel Bugzilla #7268.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Patrick Caulfield <pcaulfie@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>