netlink: specs: conntrack: fix the per-CPU stats reply

ctnetlink_ct_stat_cpu_fill_info() emits CTA_STATS_INVALID but
does not emit CTA_STATS_SEARCHED. Update the attr list, and
remove the false annotation of invalid as obsolete.

Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>
Link: https://patch.msgid.link/20260910003852.2184031-7-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>