testing: Update description and test evaluation of host2host-transport-nat

testing: Update description and test evaluation of host2host-transport-nat

As we now reuse the reqid for identical SAs, the behavior changes for
transport connections to multiple peers behind the same NAT. Instead of
rejecting the SA, we now have two valid SAs active. For the reverse path,
however, sun sends traffic always over the newer SA, resembling the behavior
before we introduced explicit SA conflicts for different reqids.