RxMacControl
CSR_WRITE_2(sc, RxMacControl, rxfilt);
rxfilt = CSR_READ_2(sc, RxMacControl);
CSR_WRITE_2(sc, RxMacControl, rxfilt);
rxfilt = CSR_READ_2(sc, RxMacControl);
CSR_WRITE_2(sc, RxMacControl, rxfilt);