tool_operate: Fix retry on FTP 4xx to ignore other protocols

Only treat response code as FTP response codes in case the
protocol type is FTP.

This fixes an issue where an HTTP download was treated as FTP
in case libcurl returned with 33. This happens when the
download has already finished and the server responses 416:
  HTTP/1.1 416 Requested Range Not Satisfiable

This should not be treated as an FTP error.

Fixes #2464
Closes #2465