Enhance FTP Sampler/Jmeter client to support for Passive(PASV) mode

**Balaji Iyer** ([Bug 52948](https://bz.apache.org/bugzilla//show_bug.cgi?id=52948&redirect=false)):
Could we enhance FTP sampler/Jmeter client to support Passive(PASV)mode?
On one of the occasions, I had this requirement of connecting to a SFTP server from Jmeter and was suggested to route the traffic from Jmeter to SFTP server via "Stunnel".
For the client to work via the tunnel it had to function in the PASV Mode which is not supported by the client.
Would be great if we could enhance the client to support PASV mode.

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