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>
1 file changed