In PASV mode, the FTP server returns its server IP (eg. pasv_address in vsftpd.conf),
when clients are from different subnets through NAT, they expect different server IP.
This patch exposes the workaround in commons-ftp into commons-vfs:
- use EPSV mode instead of PASV mode, EPSV mode returns only server port
- use PASV mode but overwrite the returned server IP with HostnameResolver