DEFLATE_OVHD
wptr += DEFLATE_OVHD;
olen = PPP_HDRLEN + DEFLATE_OVHD;
if (isize <= PPP_HDRLEN + DEFLATE_OVHD) {
state->strm.next_in = ibuf + PPP_HDRLEN + DEFLATE_OVHD;
state->strm.avail_in = isize - (PPP_HDRLEN + DEFLATE_OVHD);