ftp/tnftp: Update to 20260211

Changes since tnftp 20230507:

• Improve transfer performance by simplifying socket buffer and transfer buffer handling.
• Add -b BUFLEN to adjust size of buffer for HTTP response line parsing.
• Add -h HEADER to support custom HTTP headers.
• Add "connect" as a synonym for "open".
• Fix ASCII mode transfers when progress bar is enabled.
• Fix creation of empty downloaded files.
• Exit non-zero if a HTTP transfer is shorter than expected.
• Fix HTTPS through a proxy.

MFH: 2026Q1
(cherry picked from commit 4c34855088baa6c1fc6ea52475cd36182dc113ca)