INP_HDRINCL
sotoinpcb(so)->inp_flags |= INP_HDRINCL;
if ((inp->inp_flags & INP_HDRINCL) == 0) {
inp->inp_flags |= INP_HDRINCL;
inp->inp_flags &= ~INP_HDRINCL;
*mtod(m, int *) = inp->inp_flags & INP_HDRINCL;