cfpkt_peek_head
int cfpkt_peek_head(struct cfpkt *pkt, void *data, u16 len);
cfpkt_peek_head(pkt, &linktype, 1);
cfpkt_peek_head(pkt, &linkid, 1);
if (cfpkt_peek_head(pkt, rfml->seghead, 6) != 0)
err = cfpkt_peek_head(pkt, head, 6);
cfpkt_peek_head(pkt, &tmp, 2);