dlm: Do not allocate a fd for peeloff

avoids allocating a fd that a) propagates to every kernel thread and
usermodehelper b) is not properly released.

References: http://article.gmane.org/gmane.linux.network.drbd/22529
Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>