MTW_DMA_PAD
memset(txd->buf + xferlen, 0, MTW_DMA_PAD);
memset(sc->txd_fw->buf + len, 0, MTW_DMA_PAD);
xferlen = len + sizeof(struct mtw_txd) + MTW_DMA_PAD;
m1->m_pkthdr.len = m1->m_len = dmalen + MTW_DMA_PAD;
offset += dmalen + sizeof(struct mtw_rxd) + MTW_DMA_PAD;
usbd_frame_zero(pc, size, ((-size) & 3) + MTW_DMA_PAD);
size += ((-size) & 3) + MTW_DMA_PAD;
len = data->len + sizeof(struct mtw_txd) + MTW_DMA_PAD;