title: JAVA FTPSClient file listing issue
body: <p>I am using apache commons-net 3.6 library to connect FTPS server. FTPS server is behind NAT of thirdparty. and I can't change any settings on server side.
  I can login to server, but can not list files. I've tried same code with some public FTP and FTPS servers, and result was successfull. Seems that they are not behind NAT. But filezilla can successfully connect and list files from my problematic server.
  There is my code</p>
  
  <pre><code>       ftps.connect(server, port);
         System.out.println("Connected to " + server + ".");
  
          reply = ftps.getReplyCode();
          ftps.enterLocalPassiveMode();
          if (!FTPReply.isPositiveCompletion(reply)) {
              ftps.disconnect();
              System.err.println("FTP server refused connection.");
              System.exit(1);
          }
          if (!ftps.login(username, password)) {
              ftps.logout();
  
          }
        //  ftps.setEnabledSessionCreation(false);
          ftps.feat();
          ftps.execPBSZ(0);
          ftps.execPROT("P");
          ftps.setFileType(FTP.BINARY_FILE_TYPE);  
          FTPFile dirs[] = ftps.listDirectories();
  </code></pre>
  
  <p>And there is my ftps log:</p>
  
  <pre><code>220 FTP Server ready.
  AUTH TLS
  234 AUTH TLS successful
  Connected to x.x.x.x
  USER *******
  331 Password required for azercell
  PASS *******
  230 User myuser logged in
  FEAT
  211-Features:
   MDTM
   MFMT
   LANG bg-BG;en-US;fr-FR;it-IT;ja-JP;ko-KR;ru-RU;zh-CN;zh-TW
   TVFS
   UTF8
   AUTH TLS
   MFF modify;UNIX.group;UNIX.mode;
   MLST modify*;perm*;size*;type*;unique*;UNIX.group*;UNIX.mode*;UNIX.owner*;
   PBSZ
   PROT
   REST STREAM
   SIZE
  211 End
  PBSZ 0
  200 PBSZ 0 successful
  PROT P
  200 Protection set to Private
  TYPE I
  200 Type set to I
  SYST
  215 UNIX Type: L8
  PASV
  227 Entering Passive Mode (192,168,2,50,192,12).
  [Replacing PASV mode reply address 192.168.2.50 with x.x.x.x]
  LIST
  150 Opening BINARY mode data connection for file list
  425 Unable to build data connection: Operation not permitted
  </code></pre>
  
  <p>I'd  read that prior to version 3.6 commons-net library prior couldnt handle behind NAT connections properly.</p>
  
  <p>Can anyone help me? What is wrong with my code?</p>