Use the new isNetworkSupported api for wifi-only

Didn't have an API for this before so people used a hacked system property (ro.carrier)
to determine if the device supported mobile data.  Added new API and switching callsites.

bug:5087537
Change-Id: Ibd799559be102a9e2fd552d1a23d1afbcf8f4614

src/com/android/settings/wifi/AdvancedWifiSettings.java

@@ -97,7 +97,7 @@ public class AdvancedWifiSettings extends SettingsPreferenceFragment
 
         ListPreference sleepPolicyPref = (ListPreference) findPreference(KEY_SLEEP_POLICY);
         if (sleepPolicyPref != null) {
-            if (Utils.isWifiOnly()) {
+            if (Utils.isWifiOnly(getActivity())) {
                 sleepPolicyPref.setEntries(R.array.wifi_sleep_policy_entries_wifi_only);
                 sleepPolicyPref.setSummary(R.string.wifi_setting_sleep_policy_summary_wifi_only);
             }