trafgen: fix command line option

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
trafgen: use stddef defines in example

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
trafgen: minor: fix smoke test description

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