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: ba0f7806

 ("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>