NGBE_RDB_PB_SZ
fcrth = NGBE_READ_REG(hw, NGBE_RDB_PB_SZ) - 24576;
rx_pba = NGBE_READ_REG(&sc->hw, NGBE_RDB_PB_SZ) >> NGBE_RDB_PB_SZ_SHIFT;
NGBE_WRITE_REG(hw, NGBE_RDB_PB_SZ, rxpktsize);