dlm: fix lowcomms_connect_node for sctp

The recently added dlm_lowcomms_connect_node() from
391fbdc5d527149578490db2f1619951d91f3561 does not work
when using SCTP instead of TCP.  The sctp connection code
has nothing to do without data to send.  Check for no data
in the sctp connection code and do nothing instead of
triggering a BUG.  Also have connect_node() do nothing
when the protocol is sctp.

Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/lowcomms.c

@@ -316,6 +316,10 @@ int dlm_lowcomms_connect_node(int nodeid)
 {
 	struct connection *con;
 
+	/* with sctp there's no connecting without sending */
+	if (dlm_config.ci_protocol != 0)
+		return 0;
+
 	if (nodeid == dlm_our_nodeid())
 		return 0;
 
@@ -855,11 +859,14 @@ static void sctp_init_assoc(struct connection *con)
 	outmessage.msg_flags = MSG_EOR;
 
 	spin_lock(&con->writequeue_lock);
-	e = list_entry(con->writequeue.next, struct writequeue_entry,
-		       list);
 
-	BUG_ON((struct list_head *) e == &con->writequeue);
+	if (list_empty(&con->writequeue)) {
+		spin_unlock(&con->writequeue_lock);
+		log_print("writequeue empty for nodeid %d", con->nodeid);
+		return;
+	}
 
+	e = list_first_entry(&con->writequeue, struct writequeue_entry, list);
 	len = e->len;
 	offset = e->offset;
 	spin_unlock(&con->writequeue_lock);