- Send msg 6 even if msg 5 is not received, after a short delay, to detect symmetric NAT
- Prevent test result of symmetric NAT if Charlie is the one that appears to be symmetric natted.
- Mark if Charlie unreachable if apparently symmetric natted.
- Do not treat a different IP but same port as symmetric NAT
- Increase msg 6 retransmission frequency
- Ignore msg 5 received after sending msg 6
- Call externalAddressReceived() on reception of msg 7
- Add javadoc for testComplete() state machine

Most changes only affect SSU2; some SSU1 changes to follow.

ref: http://zzz.i2p/topics/3489