Properly fix the timekeeping overflow detection

Properly fix the timekeeping overflow detection

The underlying issue was a mismatch between the ring buffer
configuration description of the number of clock bits (32) saved and the
actual number used (27).

Introduce LTTNG_COMPACT_EVENT_BITS and LTTNG_COMPACT_TSC_BITS across the
code to remove all hardcoded instances of these values to ensure this
kind of mistake does not happen again.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reported-by: Sébastien Barthélémy <barthelemy@crans.org>