netsniff-ng: Fix whitespaces

Remove some leading/trailing whitespaces.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
trafgen: Don't expose -k/--kernel-pull anymore and warn if it still used

The -k/--kernel-pull option got useless with commit c139e80 ("trafgen:
remove timer-based trigger model"). Instead of entirely removing it and
thus possibly breaking people's scripts, still accept it as an option,
but warn the user about it. We might want to remove the option in a
future release.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>