Add @file markers for epan headers so that Doxygen will generate documentation for them.
Change-Id: I4cc99cef1e52fcce308608dd95befa2286787b16 Reviewed-on: https://code.wireshark.org/review/35728 Petri-Dish: Jörg Mayer <jmayer@loplof.de> Tested-by: Petri Dish Buildbot Reviewed-by: Jaap Keuter <jaap.keuter@xs4all.nl> Reviewed-by: Guy Harris <guy@alum.mit.edu>