javadoc fixes part 7 (ticket #1894)

core/java/src/gnu/getopt/Getopt.java

core/java/src/net/i2p/client/naming/NamingService.java

core/java/src/net/i2p/crypto/ElGamalAESEngine.java

core/java/src/net/i2p/crypto/eddsa/math/GroupElement.java

core/java/src/net/i2p/data/Certificate.java

core/java/src/net/i2p/data/PrivateKeyFile.java

core/java/src/net/i2p/util/EepGet.java

router/java/src/net/i2p/data/i2np/FastI2NPMessageImpl.java

router/java/src/net/i2p/data/i2np/I2NPMessageImpl.java

router/java/src/net/i2p/router/tasks/ThreadDump.java