kernel: extract kmod-sched-act-ipt from kmod-sched

kernel: extract kmod-sched-act-ipt from kmod-sched

There is only one module in kmod-sched that depends on iptables. Move it
to its own kmod package so we can drop the kmod-ipt-core dependency from
kmod-sched. This makes it possible to disable all kmod-ipt-* packages
without having to disable kmod-sched. Since we now default to firewall4
and nftables, we should avoid iptables dependencies where we can.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>