SSU2: Implement peer test state machine

.../net/i2p/router/transport/udp/InboundEstablishState2.java

router/java/src/net/i2p/router/transport/udp/PeerState2.java

.../java/src/net/i2p/router/transport/udp/PeerTestEvent.java

...ava/src/net/i2p/router/transport/udp/PeerTestManager.java

.../java/src/net/i2p/router/transport/udp/PeerTestState.java

...er/java/src/net/i2p/router/transport/udp/SSU2Payload.java

router/java/src/net/i2p/router/transport/udp/SSU2Util.java

...r/java/src/net/i2p/router/transport/udp/UDPTransport.java