HADOOP-18561. Update commons-net to 3.9.0 (#5214)


Addresses CVE-2021-37533, which *only* relates to FTP.

Applications not using the ftp:// filesystem, which, as
anyone who has used it will know is very minimal and
so rarely used, is not a critical part of the project.

Furthermore, the FTP-related issue is at worst information leakage
if someone connects to a malicious server.

This is a due diligence PR rather than an emergency fix.

Contributed by Steve Loughran

2 files changed