i2ptunnel: Add subsession support to servers, no UI yet

Update subsession javadocs

apps/streaming/java/src/net/i2p/client/streaming/impl/I2PSocketManagerFull.java

@@ -236,6 +236,10 @@ public class I2PSocketManagerFull implements I2PSocketManager {
     }
     
     /**
+     *  For a server, you must call connect() on the returned object.
+     *  Connecting the primary session does NOT connect any subsessions.
+     *  If the primary session is not connected, connecting a subsession will connect the primary session first.
+     *
      *  @return a new subsession, non-null
      *  @param privateKeyStream null for transient, if non-null must have same encryption keys as primary session
      *                          and different signing keys