Add unaudited exported flag to exposed runtime receivers

Android T allows apps to declare a runtime receiver as not exported
by invoking registerReceiver with a new RECEIVER_NOT_EXPORTED flag;
receivers registered with this flag will only receive broadcasts from
the platform and the app itself. However to ensure developers can
properly protect their receivers, all apps targeting U or later
registering a receiver for non-system broadcasts must specify either
the exported or not exported flag when invoking #registerReceiver;
if one of these flags is not provided, the platform will throw a
SecurityException. This commit updates all the exposed receivers
with a new RECEIVER_EXPORTED_UNAUDITED flag to maintain the existing
behavior of exporting the receiver while also flagging the receiver
for audit before the U release.

Bug: 234659204
Test: Build
Change-Id: I8fbcf69575d829f26e02d661498d69f5fc8740d0

src/com/android/settings/network/TetherEnabler.java

@@ -166,7 +166,8 @@ public class TetherEnabler implements SwitchWidgetController.OnSwitchChangeListe
                 TetheringManager.ACTION_TETHER_STATE_CHANGED);
         filter.addAction(WifiManager.WIFI_AP_STATE_CHANGED_ACTION);
         filter.addAction(BluetoothAdapter.ACTION_STATE_CHANGED);
-        mContext.registerReceiver(mTetherChangeReceiver, filter);
+        mContext.registerReceiver(mTetherChangeReceiver, filter,
+                Context.RECEIVER_EXPORTED/*UNAUDITED*/);
         mTetheringEventCallback  =
                 new TetheringManager.TetheringEventCallback() {
                     @Override