dlm: set zero linger time on sctp socket

The recovery time for a failed node was taking a long
time because the failed node could not perform the full
shutdown process.  Removing the linger time speeds this
up.  The dlm does not care what happens to messages to
or from the failed node.

Signed-off-by: Dongmao Zhang <dmzhang@suse.com>
Signed-off-by: David Teigland <teigland@redhat.com>