message: fix: increase stack size of protocol handler threads
  Since we have more method calls starting from
  OnSessionStartedCallback(), we may encounter a stack overflow
  issue (tested on Ubuntu 16.04 x86_64 box). The stack size is
  increased to avoid such issue.
diff: @@ -57,7 +57,7 @@ CREATE_LOGGERPTR_GLOBAL(logger_, "ProtocolHandler")
  std::string ConvertPacketDataToString(const uint8_t* data,
  const size_t data_size);
  -const size_t kStackSize = 32768;
  +const size_t kStackSize = 65536;
  ProtocolPacket::ProtocolVersion defaultProtocolVersion(5, 0, 0);
  