Transports: Consolidate port checking code

router/java/src/net/i2p/router/transport/TransportUtil.java

...java/src/net/i2p/router/transport/ntcp/NTCPTransport.java

...rc/net/i2p/router/transport/udp/EstablishmentManager.java

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

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

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

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