SLIP_HDRLEN
#define BUFOFFSET (128+sizeof(struct ifnet **)+SLIP_HDRLEN)
bpfattach(&sc->sc_if, DLT_SLIP, SLIP_HDRLEN);
u_char bpfbuf[SLTMAX + SLIP_HDRLEN];
u_char *cp = bpfbuf + SLIP_HDRLEN;
len + SLIP_HDRLEN);
u_char *hp = sc->sc_buf - SLIP_HDRLEN;
len + SLIP_HDRLEN);