void pcnet_reset(paddr_t base, int mmap);
Ensure that a PCnet-style Ethernet controller chip at the given physical address (either I/O or memory-mapped as specified by mmap) is disabled. Some ROM monitors leave the Ethernet receiver enabled after downloading the OS image. This causes memory to be corrupted after the system starts and before Neutrino's Ethernet driver is run, due to the reception of broadcast packets. This function makes sure that no further packets are received by the chip until the Neutrino driver starts up and properly initializes it.