Update Wifi Tether band selection UI

This CL updates the preference for selecting the enabled tether bands
to allow individual selection of multiple bands instead of forcing
a single selection. Note that while this makes the UI theoretically
support new bands in the future, the wifi backend only supports
selecting a single band or all bands which this CL does not address.

Test: robotests
Bug: 73102003
Change-Id: Ib2d4a2834c5cd11875515d308f7b20bfc8471959

res/layout/hotspot_ap_band_selection_dialog.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2018 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:orientation="vertical"
+    android:padding="8dp"
+    android:paddingStart="@dimen/wifi_ap_band_checkbox_padding">
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:paddingStart="8dp"
+        android:text="@string/wifi_ap_band_select_one"
+        android:textAppearance="?android:attr/textAppearanceSmall"/>
+
+    <CheckBox
+        android:id="@+id/box_2g"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_marginBottom="@dimen/wifi_ap_band_checkbox_padding"
+        android:layout_marginTop="@dimen/wifi_ap_band_checkbox_padding"
+        android:paddingStart="@dimen/wifi_ap_band_checkbox_padding"
+        android:textAppearance="?android:attr/textAppearanceMedium"/>
+
+    <CheckBox
+        android:id="@+id/box_5g"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:paddingStart="@dimen/wifi_ap_band_checkbox_padding"
+        android:textAppearance="?android:attr/textAppearanceMedium"/>
+</LinearLayout>