UDP 20/21 ports allowed by default

[unihostbrasil]

The default CSF configuration files allow UDP in/out ports 20 and 21:

UDP_IN/UDP6_IN = "20,21..."
UDP_OUT/UDP6_OUT = "20,21..."

I believe this is a mistake. The FTP RFC defines it as a TCP-only protocol.
https://www.rfc-editor.org/rfc/rfc959

We were also unable to locate any implementation of ports 20,21/UDP in the field.