Fixed the bug that prevented communication with FTP servers behind
NAT in extended passive mode if the server's public IP address was
different from the main NAT address. This caused a wrong aliasing
link to be created that did not route the incoming packets back to
the original IP address of the server.

natd -v -n pub0 -redirect_address localFTP publicFTP

Note that even if localFTP == publicFTP, one still needs to supply
the -redirect_address directive. It is needed as a helper because
extended passive mode's 229 reply does not contain the IP address.

MFC after: 1 week