+ * There are two encap possibilities
+ * 1) the tunnel and ths SA are prodiving encap, i.e. it's
+ * MAC | SA-IP | TUN-IP | ESP | PAYLOAD
+ * implying the SA is in tunnel mode (on a tunnel interface)
+ * 2) only the tunnel provides encap
+ * MAC | TUN-IP | ESP | PAYLOAD
+ * implying the SA is in transport mode.
+ *
+ * For 2) we need only strip the tunnel encap and we're good.
+ * since the tunnel and crypto ecnap (int the tun=protect
+ * object) are the same and we verified above that these match
+ * for 1) we need to strip the SA-IP outer headers, to
+ * reveal the tunnel IP and then check that this matches
+ * the configured tunnel.