tcp_metrics: use parallel_ops for tcp_metrics_nl_family

TCP_METRICS_CMD_GET and TCP_METRICS_CMD_DEL use their
own locking (tcp_metrics_lock and RCU),
they do not need genl_mutex protection.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240416162025.1251547-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_metrics.c

@@ -988,6 +988,7 @@ static struct genl_family tcp_metrics_nl_family __ro_after_init = {
 	.maxattr	= TCP_METRICS_ATTR_MAX,
 	.policy = tcp_metrics_nl_policy,
 	.netnsok	= true,
+	.parallel_ops	= true,
 	.module		= THIS_MODULE,
 	.small_ops	= tcp_metrics_nl_ops,
 	.n_small_ops	= ARRAY_SIZE(tcp_metrics_nl_ops),