See http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=202475. To fix this, just apply the supplied patch. It follows the latest instructions from the FSF for using GPL. This is the easiest course, costs you nothing, and will probably result in the inclusion of GNU netcat in debian.
(I am not involved in debian. I just decided to find out about netcat, read http://en.wikipedia.org/wiki/Netcat, wondered why a GNU netcat was created, and looked into it, finding the debian bug report, so I decided to fix the problem and submit a patch, instead of asking you to do the dirty work of editing the licensing stuff as the debian guys did, without reply).
The supplied patch also fixes an error which prevents the HTML document from building.
If you would prefer less drastic changes, such as not switching to GPL3 and not using the UTF-8 copyright character, I am perfectly willing to make a different patch to your specifications. I just followed the latest best practices, which have changed since 2004.
IMHO, the GNU FDL is not appropriate for a document where including a copy of the license in the document, as required by the license, increases the size of the document by a noticeable amount. Also, using it annoys the debian folks, and using invariant sections keeps you out of debian.
But if you want to use it, the FSF now recommends including text of the license in a section NOT MARKED INVARIANT.
Presently, you specify that the section is invariant, but don't even include the section. The easiest fix is just switch the small document from GFDL to GPL.
(I notice the submit button is called "Add Artifact." I hope this creates a new bug report and not an attachment to some other bug...)