only              299 dev/ic/xlreg.h #define XL_MACCTRL_EXTEND_AFTER_COL	0x0080 (3c905B only)
only              300 dev/ic/xlreg.h #define XL_MACCTRL_FLOW_CONTROL_ENB	0x0100 (3c905B only)
only              301 dev/ic/xlreg.h #define XL_MACCTRL_VLT_END		0x0200 (3c905B only)