Fix: compaction instrumentation update for 3.14.x stable kernels

Conditional compilation introduced by lttng-modules commit

  0007344741ef65259bc52dea72259173dfbf96c0

needs to be applied to kernels 3.14.25 and up in the 3.14.x branch.

Squashed with commit 0007344741ef65259bc52dea72259173dfbf96c0 which was
originally targetting 3.16.

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Reported-by: Bjørn Forsman <bjorn.forsman@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>