Timestamp adjustment function
#include <dtk_time.h>
int dtk_addtime(struct dtk_timespec* ts, long sec, long nsec);
The function dtk_addtime() adjusts the time pointed by ts by adding sec seconds and nsec nanoseconds.
On success, the function returns 0, otherwise -1.
dtk_addtime() will fail if:
EINVAL
The value in the nsec field was not in the range -999999999 to 999999999.