Ignore EINTR from usleep(3) in try_locks(..)

NetBSD's usleep(3) only returns -1/sets errno=EINVAL when `microseconds`
is one million or more

MFC after: 3 days
Submitted by: pho
Sponsored by: EMC / Isilon Storage Division

contrib/netbsd-tests/kernel/t_lockf.c

@@ -102,6 +102,9 @@ trylocks(int id)
 		(void)fcntl(fd, F_SETLKW, &fl);
 
 		if (usleep(sleeptime) < 0) 
+#if defined(__FreeBSD__)
+		  if (errno != EINTR)
+#endif
 		  err(1, "usleep");
 	}
 	printf("%d: done\n", id);