PPP_CONTROL
*wptr++ = PPP_CONTROL(rptr); /* all in one mbuf */
ctrl = PPP_CONTROL(rptr);
ctrl = PPP_CONTROL(cp);
control = PPP_CONTROL(dst->sa_data);
control = PPP_CONTROL(cp);
wptr[1] = PPP_CONTROL(rptr);
wptr[1] = PPP_CONTROL(hdr);