neighbour: fix neigh_master_filtered()

If we no longer hold RTNL, we must use netdev_master_upper_dev_get_rcu()
instead of netdev_master_upper_dev_get().

Fixes: ba0f780 ("neighbour: no longer hold RTNL in neigh_dump_info()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240421185753.1808077-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/neighbour.c

@@ -2682,7 +2682,7 @@ static bool neigh_master_filtered(struct net_device *dev, int master_idx)
 	if (!master_idx)
 		return false;
 
-	master = dev ? netdev_master_upper_dev_get(dev) : NULL;
+	master = dev ? netdev_master_upper_dev_get_rcu(dev) : NULL;
 
 	/* 0 is already used to denote NDA_MASTER wasn't passed, therefore need another
 	 * invalid value for ifindex to denote "no master".