net: sched: incorrect Kconfig dependencies on Netfilter modules

- NET_ACT_CONNMARK and NET_ACT_CTINFO only require conntrack support.
- NET_ACT_IPT only requires NETFILTER_XTABLES symbols, not
  IP_NF_IPTABLES. After this patch, NET_ACT_IPT becomes consistent
  with NET_EMATCH_IPT. NET_ACT_IPT dependency on IP_NF_IPTABLES predates
  Linux-2.6.12-rc2 (initial git repository build).

Fixes: 22a5dc0e ("net: sched: Introduce connmark action")
Fixes: 24ec483c

 ("net: sched: Introduce act_ctinfo action")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Link: https://lore.kernel.org/r/20201208204707.11268-1-pablo@netfilter.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>