[DCCP]: Reduce the number of writable states

Since DCCP requires to close both ends of a connection simultaneously,
permission to write in state DCCP_CLOSING is removed in dccp_sendmsg():
 * if the sending end closed, it would encounter a write error anyhow;
 * if the other end has closed the connection, it accepts no more data.
Signed-off-by: NGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: NIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: NArnaldo Carvalho de Melo <acme@ghostprotocols.net>

net/dccp/proto.c

@@ -664,7 +664,7 @@ int dccp_sendmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	 * so that the trick in dccp_rcv_request_sent_state_process.
 	 */
 	/* Wait for a connection to finish. */
-	if ((1 << sk->sk_state) & ~(DCCPF_OPEN | DCCPF_PARTOPEN | DCCPF_CLOSING))
+	if ((1 << sk->sk_state) & ~(DCCPF_OPEN | DCCPF_PARTOPEN))
 		if ((rc = sk_stream_wait_connect(sk, &timeo)) != 0)
 			goto out_release;