When we are doing SA lookup for TCP-MD5, check both source and
destination addresses. Previous code has used only destination address
for lookup. But for inbound packets the source address was used as SA
destination address. Thus only outbound SA were used for both directions.
Now we use addresses from a packet as is, thus SAs for both directions are
needed.

Reported by:	Mike Tancsa

In the example section show that TCP-MD5 connection needs SA for both
directions.
Use unique SPI.