build_packet
ssize_t build_packet(uint8_t, struct iface *, char *);
pkt_len = build_packet(message_type, iface, if_name);
pkt_len = build_packet(message_type, iface->ifinfo.if_name, iface->xid,
ssize_t build_packet(uint8_t, char *, uint32_t, struct ether_addr *,
build_packet(ra_iface);
int build_packet(struct ra_iface *);
if (build_packet(ra_iface)) {