fixing #3568

git-svn-id: https://gnunet.org/svn/gnunet@34496 140774ce-b5e7-0310-ab8b-a85725594a96
-zero-terminate

git-svn-id: https://gnunet.org/svn/gnunet@34497 140774ce-b5e7-0310-ab8b-a85725594a96
-fix FIXMEs

git-svn-id: https://gnunet.org/svn/gnunet@34498 140774ce-b5e7-0310-ab8b-a85725594a96
-sending session ID back over same CADET channel is redundant

git-svn-id: https://gnunet.org/svn/gnunet@34499 140774ce-b5e7-0310-ab8b-a85725594a96
-simplify further, too much checking...

git-svn-id: https://gnunet.org/svn/gnunet@34500 140774ce-b5e7-0310-ab8b-a85725594a96
-clarify docs

git-svn-id: https://gnunet.org/svn/gnunet@34501 140774ce-b5e7-0310-ab8b-a85725594a96
-indentation, doxygen

git-svn-id: https://gnunet.org/svn/gnunet@34502 140774ce-b5e7-0310-ab8b-a85725594a96