Weird error. However, I just seem to fix my "hard lockups". In if_cs_send_data() I need to call if_cs_disable_ints() / if_cs_enable_ints(). After I did this, I can now run "scp test.iso 10.2.1.4:/tmp" and "while true; do iwconfig eth1; sleep 0.2; done" simultanously.