Fix for multi-apn MMS access.

Mark cellular variants with the same availability, regardless of which are currently in use.
Availability just means the radio is enabled and sees the network, but has no guarantees that
we could connect to an APN if requested.

Fix the requestRouteToHost logic to support apn switches without WIFI.

bug:2093841

core/java/android/net/NetworkInfo.java

@@ -131,7 +131,7 @@ public class NetworkInfo implements Parcelable {
         mSubtypeName = subtypeName;
         setDetailedState(DetailedState.IDLE, null, null);
         mState = State.UNKNOWN;
-        mIsAvailable = true;
+        mIsAvailable = false; // until we're told otherwise, assume unavailable
         mIsRoaming = false;
     }