Create new isNetworkSupported API

Useful for checking if on a wifi-only device.
Similar to asking for NetworkInfo for a network type and checking for
null, though here the intent is explicit.

bug:5087537
Change-Id: Ia3ddd09b6b735b8b3ceb7a347891e015fd96b218
diff --git a/services/java/com/android/server/SystemServer.java b/services/java/com/android/server/SystemServer.java
index d0e8b5e..2714fc5 100644
--- a/services/java/com/android/server/SystemServer.java
+++ b/services/java/com/android/server/SystemServer.java
@@ -350,7 +350,6 @@
                 Slog.i(TAG, "Wi-Fi Service");
                 wifi = new WifiService(context);
                 ServiceManager.addService(Context.WIFI_SERVICE, wifi);
-                wifi.checkAndStartWifi();
             } catch (Throwable e) {
                 reportWtf("starting Wi-Fi Service", e);
             }
@@ -361,6 +360,7 @@
                 ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);
                 networkStats.bindConnectivityManager(connectivity);
                 networkPolicy.bindConnectivityManager(connectivity);
+                wifi.checkAndStartWifi();
                 wifiP2p.connectivityServiceReady();
             } catch (Throwable e) {
                 reportWtf("starting Connectivity Service", e);