util/time: make NSEC_PER_SEC static
This fixes static linking with libseat.
Closes
#include "util/time.h"
-const long NSEC_PER_SEC = 1000000000;
+static const long NSEC_PER_SEC = 1000000000;
int64_t timespec_to_msec(const struct timespec *a) {
return (int64_t)a->tv_sec * 1000 + a->tv_nsec / 1000000;
