Make OS_ReadSysInfo(4) only return a unicast MAC
Recent issues on some Pi3 kit using the EtherUSB module showed that the return of OS_ReadSysInfo(4) included the multicast bit (r0 bit 0) set. This is not wise and causes problems with modern internet stacks. If the address is read from the network card or HAL, or is generated from the Acorn ID chip the return is untouched. The last ditch is to generate one from the machine random generated ID if it has one. Bit 0 is now clear and bit 1 is now set in the address thus generated. Bit 0 is unicast/multicast, 0 being unicast. Bit 1 set indicates a locally allocated address rather than a globally allocated one.