Bring up interface first before setting the frequency

This is also needed when setting up monitor interface for sending
management frames.

BUG=chrome-os-partner:32216
TEST=Run network_WiFi_ChannelScanDwellTime
DEPLOY=test_importer

Change-Id: Ia0fe387d64424d140d91cc3c28d4ad573f2275d9
Reviewed-on: https://chromium-review.googlesource.com/220650
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Peter Qiu <zqiu@chromium.org>
Tested-by: Peter Qiu <zqiu@chromium.org>
diff --git a/server/site_linux_router.py b/server/site_linux_router.py
index aa20bef..7aca203 100644
--- a/server/site_linux_router.py
+++ b/server/site_linux_router.py
@@ -744,8 +744,8 @@
         frequency = hostap_config.HostapConfig.get_frequency_for_channel(
                 channel)
         interface = self.get_wlanif(frequency, 'monitor')
-        self.iw_runner.set_freq(interface, frequency)
         self.router.run('%s link set %s up' % (self.cmd_ip, interface))
+        self.iw_runner.set_freq(interface, frequency)
         return interface