Core/NetworkIO: Fix performance loss when handling bad packets

Revert f9cb4280bd8f1c29e4acbae5339bce40c3b52bcb which retrieved the callstack each time a ByteBufferPositionException or a ByteBufferSourceException occurred, for example with bad packet structure.
2014_05_28-Playerbot_NPCBots

Signed-off-by: Lavrentyi Tritonovich <lavrentyi.sleepwalker@gmail.com>