or, fly a C-17 sized aircraft at FL400 over the anti-anti-anti-droneswarm and drop many metric tons of unspooled fine gauge fishing line. More seriously though, if small drone swarms will be limited in the altitudes that they can reach (being limited by battery life, not enough motor runtime to ascend to FL200, travel laterally, and then down to a ground attack again, for instance), any modern air force that can establish air superiority over a battlefield... Will have a lot of different options to attack drone swarms from above.