Fixed the bug that prevented communication with FTP servers behind

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