[EXT] [PATCH] ipsec: fix NAT-T length calculation

[Xiao Liang]

> sa->hdr_len and prm->tun.hdr_len don't include L2 length so both should
> start in the diagram at the end of the ETH header.
>
> So the right way to compute datagram length is
>
> dgram_len = mb->pkt_len - sqh_len - sa->hdr_l3_off - sa->hdr_len +
> sizeof(struct rte_udp_hdr)
>

|<-           mb->pkt_len - sqh_len                   ->|
|<- sa->hdr_l3_off ->|<- sa->hdr_len ->|
                                  |<- udph->dgram_len ->|

+--------------------+------------+-----+-----+---------+-----+
|         ETH        |     IP     | UDP | ESP | payload | sqh |
+--------------------+------------+-----+-----+---------+-----+

|<- sa->hdr_l3_off ->|<- l3_len ->|
                     |<- sa->hdr_len  ->|

If hdr_len doesn't include L2 length, I would agree that

    dgram_len = mb->pkt_len - sqh_len - sa->hdr_l3_off - sa->hdr_len +
sizeof(struct rte_udp_hdr)

But then what's the point of
    sa->hdr_len - sa->hdr_l3_off
in lib/ipsec/sa.c?