net: document NETDEV_CHANGENAME as ops locked

NETDEV_CHANGENAME is only emitted from netif_change_name().
netif_change_name() has two callers both of which hold netdev_lock_ops()
around the call site:
 - dev_change_name()
 - do_setlink()

Document NETDEV_CHANGENAME as always ops locked.

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260603012840.2254293-4-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/netdevices.rst

@@ -415,6 +415,7 @@ The following netdev notifiers are always run under the instance lock:
 For devices with locked ops, currently only the following notifiers are
 running under the lock:
 * ``NETDEV_CHANGE``
+* ``NETDEV_CHANGENAME``
 * ``NETDEV_REGISTER``
 * ``NETDEV_UP``
 

net/core/lock_debug.c

@@ -65,6 +65,7 @@ int netdev_debug_event(struct notifier_block *nb, unsigned long event,
 		break;
 
 	case NETDEV_CHANGENAME:
+		netdev_assert_locked_ops(dev);
 		ASSERT_RTNL_NET(net);
 		break;
 	}