[issue32572] Add the ftplib option, overrides the IP address.

[Hideyuki]

Hideyuki <studioes at go64.jp> added the comment:

I understand that it is best to use PASV.
But this FTP server is managed by another person, and that server required active mode. 
Also, my host is in a VPC environment, it is connected by 1:1 NAT. This NAT BOX does not support FTP transparent.

In this case, we recognize that IP packet received by the FTP server is from the external IP address of the NAT BOX, but ftplib will send the IP address on host NIC.
So dose not match IP packet source address and PORT address, it will be closed with the indicated code.

The purpose of this feature is to communicate by overriding the IP address sending by PORT command with the NAT external IP address(so the client IP address seen by server).

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32572>
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