RTL8365MB_L2_MC_D4_IGMPIDX_MSK
mc->igmpidx = FIELD_GET(RTL8365MB_L2_MC_D4_IGMPIDX_MSK, data[4]);
data[4] |= FIELD_PREP(RTL8365MB_L2_MC_D4_IGMPIDX_MSK, mc->igmpidx);