Fixed crash on OSX 32bit clang due to wrong format string used for RakNet::Time.

RakNet crashed when NatPunchthroughClient has the debug interface enabled and is compiled with __GET_TIME_64BIT = 0, because the hard-coded format string is expecting uint64_t. No problems were observed on Windows and Linux.

Additionally, RakNet::Time was formatted as signed integer type despite being type-defined as unsigned.