ATHN_RIDX_MCS0
ATHN_RIDX_MCS0 + ic->ic_fixed_mcs;
an->ridx[ridx] = ATHN_RIDX_MCS0 + i;
#define ATHN_RIDX_MCS8 (ATHN_RIDX_MCS0 + 8)
#define ATHN_IS_HT_RIDX(ridx) ((ridx) >= ATHN_RIDX_MCS0)