4823 don't open-code NSEC2MSEC and MSEC2NSEC

*** 669,679 ****
                                  if ((ln = read(infd, obuf, ZLOGIN_BUFSIZ)) > 0)
                                          (void) write(STDOUT_FILENO, obuf, ln);
  
                                  /* sleep for 10 milliseconds */
                                  rqtp.tv_sec = 0;
!                                 rqtp.tv_nsec = 10 * (NANOSEC / MILLISEC);
                                  (void) nanosleep(&rqtp, NULL);
                                  if (!dead)
                                          goto retry;
                          }
  
--- 669,679 ----
                                  if ((ln = read(infd, obuf, ZLOGIN_BUFSIZ)) > 0)
                                          (void) write(STDOUT_FILENO, obuf, ln);
  
                                  /* sleep for 10 milliseconds */
                                  rqtp.tv_sec = 0;
!                                 rqtp.tv_nsec = MSEC2NSEC(10);
                                  (void) nanosleep(&rqtp, NULL);
                                  if (!dead)
                                          goto retry;
                          }