ipvs: some service readers can use RCU

ipvs: some service readers can use RCU

Some places walk the services under mutex but they can just use RCU:

* ip_vs_dst_event() uses ip_vs_forget_dev() which uses its own lock
  to modify dest
* ip_vs_genl_dump_services(): ip_vs_genl_fill_service() just fills skb
* ip_vs_genl_parse_service(): move RCU lock to callers
  ip_vs_genl_set_cmd(), ip_vs_genl_dump_dests() and ip_vs_genl_get_cmd()
* ip_vs_genl_dump_dests(): just fill skb

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Link: https://patch.msgid.link/20260224205048.4718-3-fw@strlen.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>