Allow wifi and ethenet connected at same time.

This will improve the user experience on Android TV devices,
see bug for details.

In addition when connecting adb to the device by ethernet
for cts, wifi will not connect, causing lots of tests to fail.
For example:
[CTS7.1]android.net.wifi.cts.WifiInfoTest#testWifiInfoProperties
[CTS7.1]android.net.cts.ConnectivityManagerTest#testConnectivityChanged_
manifestRequestOnlyPreN_shouldReceiveIntent

Use command:settings to put global wifi_data_always_on 1 to enable it.

Bug: 26102779
Test: Manual, CTS.
Change-Id: I711d93061a6bc7164d98a858912f781e1b967406