net/sched: Fix module name in Kconfig

The action modules have been prefixed with 'act_', but the Kconfig
description was not changed.

Signed-off-by: Jan Luebbe <jluebbe@debian.org>
Acked-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>