shorten the sleep in isc_nm_destroy()

when isc_nm_destroy() is called, there's a loop that waits for
other references to be detached, pausing and unpausing the netmgr
to ensure that all the workers' events are run, followed by a
1-second sleep. this caused a noticeable delay when shutting down
rndc; so the delay has now been reduced to a hundredth of a second.

lib/isc/netmgr/netmgr.c

@@ -417,9 +417,9 @@ isc_nm_destroy(isc_nm_t **mgr0) {
 		isc_nm_pause(mgr);
 		isc_nm_resume(mgr);
 #ifdef WIN32
-		_sleep(1000);
+		_sleep(10);
 #else  /* ifdef WIN32 */
-		usleep(1000000);
+		usleep(10000);
 #endif /* ifdef WIN32 */
 	}