MAX_XMIT_EXTBUF_SZ
res = rtw_os_xmit_resource_alloc(padapter, pxmitbuf, MAX_XMIT_EXTBUF_SZ + XMITBUF_ALIGN_SZ, true);
pxmitbuf->pend = pxmitbuf->pbuf + MAX_XMIT_EXTBUF_SZ;
rtw_os_xmit_resource_free(padapter, pxmitbuf, (MAX_XMIT_EXTBUF_SZ + XMITBUF_ALIGN_SZ), true);