[SSHD-1158] Don't send channel EOF after having received channel CLOSE

When the peer closes the channel, just reply with a CLOSE message.
Do not send an EOF before the CLOSE. See RFC 4254, section 5.3.[1]

[1] https://tools.ietf.org/html/rfc4254#section-5.3

sshd-core/src/main/java/org/apache/sshd/common/channel/AbstractChannel.java

@@ -547,7 +547,7 @@ public void handleClose() throws IOException {
  }
 
  try {
- if (!isEofSent()) {
+ if (!eofSent.getAndSet(true)) {
  if (debugEnabled) {
  log.debug("handleClose({}) prevent sending EOF", this);
  }
@@ -683,7 +683,7 @@ public String toString() {
  @Override
  protected void preClose() {
  if (!isEofSent()) {
- log.debug("close({}) prevent sending EOF", this);
+ log.debug("close({}) no EOF sent", this);
  }
 
  try {