DLM: use CF_CLOSE flag to stop dlm_send correctly

If reconnection fails while executing dlm_lowcomms_stop,
dlm_send will not stop.

Signed-off-by: Tadashi Miyauchi <miyauchi@toshiba-tops.co.jp>
Signed-off-by: Tsutomu Owa <tsutomu.owa@toshiba.co.jp>
Signed-off-by: David Teigland <teigland@redhat.com>