Add an explicit android:exported flag.

This is now required otherwise the package will fail to install.
The failure is preventing adb from being enabled in user builds.

Bug: 176424685
Test: Checked ADB is available without user intervention.
Change-Id: I87be39e24e08bd0c100f4263be1db40daa7cef7a
diff --git a/apps/SdkSetup/AndroidManifest.xml b/apps/SdkSetup/AndroidManifest.xml
index 76ef9ff..4824126 100644
--- a/apps/SdkSetup/AndroidManifest.xml
+++ b/apps/SdkSetup/AndroidManifest.xml
@@ -28,6 +28,7 @@
     <application>
         <activity android:name="DefaultActivity"
                 android:excludeFromRecents="true">
+                android:exported="true">
             <intent-filter android:priority="3">
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.HOME" />