Some conutries don't support 5G only hotspot. Thus band convert should
not only work for dual mode device. It should general design since it
will be country dependency.
Bug: 148924644
Bug: 148764406
Test: Manual Test, use command to force country
1. adb root && adb shell cmd wifi force-country-code enabled GB
2. Change Band Setting to 5G prefer
Turn on hotspot to check log and make sure it will enable succeed.
Test:make RunSettingsRoboTests ROBOTEST_FILTER=CodeInspectionTest
Change-Id: I7828c62ef399244531a72aa35c89b71549e0d623
561d041f7b