NAPIfied natsemi driver

I've now successfully NAPIfied the second NIC driver: natsemi.c... this was the only remaining driver that I care about, since it is used in the PC Engines WRAP embedded systems that I use as routers/bridges/wlan-gateways.

The result is that I can now get about 34kpps routed on an embedded 266MHz Geode CPU at full 148kpps 64byte single-flow udp flood on the input NIC.