man: netsniff-ng: add documentation for option

This was left forgotten during writing of the man page, so fix it
up and add missing documentation.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
man: trafgen: add initial version

Add an initial version of the trafgen man-page. There are still a couple
of TODO marked section that need to be addressed in follow-up commits.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>