Fix incorrect method call to wifiManager in Tether

In the WifiTetherApBandController the incorrect method was
being called to check if the device is 5Ghz compatible. We
were calling is5GhzBandSupported directly, but we were
supposed to call isDualBandSupported instead.

Test: robotests updated
Bug: 110793581
Change-Id: I61d3ff10abedde6196b8e29591ebfd3272dbbcd9