Line buffer hostapd log output on WiFi routers

BUG=chromium:393667
TEST=WPA_TKIP still passes.

Change-Id: Iee9ff7c4a1b426506c512817ec5b8916bba778a4
Reviewed-on: https://chromium-review.googlesource.com/209678
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Mukesh Agrawal <quiche@google.com>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
diff --git a/server/site_linux_router.py b/server/site_linux_router.py
index 1401b14..a6ee753 100644
--- a/server/site_linux_router.py
+++ b/server/site_linux_router.py
@@ -236,7 +236,7 @@
                      configuration.channel)
         self.router.run('rm %s' % log_file, ignore_status=True)
         self.router.run('stop wpasupplicant', ignore_status=True)
-        start_command = '%s -dd -t %s &> %s & echo $!' % (
+        start_command = 'stdbuf -oL %s -dd -t %s &> %s & echo $!' % (
                 self.cmd_hostapd, conf_file, log_file)
         pid = int(self.router.run(start_command).stdout.strip())
         self.hostapd_instances.append(HostapdInstance(