Say Y here to get to see options for IEEE 802.15.4 Low-Rate Wireless Personal Area Network device drivers. This option alone does not add any kernel code. If you say N, all options in this submenu will be skipped and disabled.
Say Y here to enable the fake driver that serves as an example of HardMAC device driver. This driver can also be built as a module. To do so say M here. The module will be called 'fakehard'.