pull in the active mode Pull request

[robklg]

There's a long standing PR to add support for FTP active mode (https://github.com/bolcom/libunftp/pull/104). There are some things to be added:

• we now have proxy protocol mode, if this is enabled, perhaps we either disable active mode, or
• write a warning to the logs to make the user aware that we currently don't do anything special with regards to making active mode outbound connections work from behind a proxy

Active mode is probably something we should disable by default, and have explicitly enabled by a configuration flag.