Call netdev_disconnect() to make netdev forget any of station.c's
callbacks for connections or transitions in progress or established.
Otherwise station.c will crash as soon as we're connected and try to
change interface mode:
==17601== Invalid read of size 8
==17601== at 0x11DFA0: station_disconnect_event (station.c:775)
==17601== by 0x11DFA0: station_netdev_event (station.c:1570)
==17601== by 0x115D18: netdev_disconnect_event (netdev.c:868)
==17601== by 0x115D18: netdev_mlme_notify (netdev.c:3403)
==17601== by 0x14E287: l_queue_foreach (queue.c:441)
==17601== by 0x1558B4: process_multicast (genl.c:469)
==17601== by 0x1558B4: received_data (genl.c:532)
==17601== by 0x152888: io_callback (io.c:123)
==17601== by 0x151BCD: l_main_iterate (main.c:376)
==17601== by 0x151C9B: l_main_run (main.c:423)
==17601== by 0x10FE20: main (main.c:489)
daf248e1ba