Wifi: Fix rototests for wifi tethering

This commit makes fixes to the wifi tethering rototests.
These fixes are done by using the proper encoding for the AP bands.

Bug: 146767071
Test: Run robotest
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=com.android.settings.wifi
Change-Id: I4ddf6ea9328dabed09bc23d355efa188975316b6