4823 don't open-code NSEC2MSEC and MSEC2NSEC

*** 2724,2734 ****
  }
  
  static int
  ns2ms(int64_t ns)
  {
!         return (ns / (NANOSEC / MILLISEC));
  }
  
  static int64_t
  tv2ns(struct timeval *tvp)
  {
--- 2724,2734 ----
  }
  
  static int
  ns2ms(int64_t ns)
  {
!         return (NSEC2MSEC(ns));
  }
  
  static int64_t
  tv2ns(struct timeval *tvp)
  {