int
libnet_build_ip(len, tos, id, frag, ttl, prot, saddr, daddr, payload, payload_s, buf)
                u_short len
                u_char tos
                u_short id
                u_short frag
                u_char ttl
                u_char prot
                u_long saddr
                u_long daddr
                const u_char * payload
                int payload_s
                u_char & buf
        OUTPUT:
                buf