unsigned long ipv6_frame(
&PacketBuf pkt,
const unsigned char eth_src[NET_MAC_LEN],
const unsigned char eth_dst[NET_MAC_LEN],
unsigned char next_hdr,
const &Ipv6Addr src,
const &Ipv6Addr dst,
unsigned short payload_len,
)IPv6-over-Ethernet full frame helper (Ethernet + IPv6 header, caller writes payload). Returns offset where payload should be written.