cifs: do not send tree disconnect to ipc shares

On session close, the IPC is closed and the server must release all
tcons of the session.  It doesn't matter if we send a ipc close or
not.

Besides, it will make the server to not close durable and resilient
files on session close, as specified in MS-SMB2 3.3.5.6 Receiving an
SMB2 LOGOFF Request.
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/connect.c

@@ -1557,29 +1557,25 @@ cifs_setup_ipc(struct cifs_ses *ses, struct smb3_fs_context *ctx)
 /**
  * cifs_free_ipc - helper to release the session IPC tcon
  *
- * Needs to be called everytime a session is destroyed
+ * Needs to be called everytime a session is destroyed.
+ *
+ * On session close, the IPC is closed and the server must release all tcons of the session.
+ * No need to send a tree disconnect here.
+ *
+ * Besides, it will make the server to not close durable and resilient files on session close, as
+ * specified in MS-SMB2 3.3.5.6 Receiving an SMB2 LOGOFF Request.
  */
 static int
 cifs_free_ipc(struct cifs_ses *ses)
 {
-	int rc = 0, xid;
 	struct cifs_tcon *tcon = ses->tcon_ipc;
 
 	if (tcon == NULL)
 		return 0;
 
-	if (ses->server->ops->tree_disconnect) {
-		xid = get_xid();
-		rc = ses->server->ops->tree_disconnect(xid, tcon);
-		free_xid(xid);
-	}
-
-	if (rc)
-		cifs_dbg(FYI, "failed to disconnect IPC tcon (rc=%d)\n", rc);
-
 	tconInfoFree(tcon);
 	ses->tcon_ipc = NULL;
-	return rc;
+	return 0;
 }
 
 static struct cifs_ses *