duration_subsec

calling `subsec_micros()` is more concise than this calculation

library/std/src/sys/windows/net.rs

@@ -162,7 +162,7 @@ impl Socket {
 
                 let mut timeout = c::timeval {
                     tv_sec: cmp::min(timeout.as_secs(), c_long::MAX as u64) as c_long,
-                    tv_usec: (timeout.subsec_nanos() / 1000) as c_long,
+                    tv_usec: timeout.subsec_micros() as c_long,
                 };
 
                 if timeout.tv_sec == 0 && timeout.tv_usec == 0 {