net_sched: act_nat: use RCU in tcf_nat_dump()

Also storing tcf_action into struct tcf_nat_params
makes sure there is no discrepancy in tcf_nat_act().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250709090204.797558-9-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>