The nanoseconds part of the timespec struct time_a is not always
bigger than time_b since it wraps around each second.
Use 64-bit arithmetic to compute the difference.
Merge/move duplicated code into utils.c.
This function is really doing two things. Split it into
timespec_to_ms() and timespec_abs_diff().
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>