lowpan: Add an exported flag in manifest

With b/150232615, we will need an explicit value set for the exported
flag when intent filters are present, as the default behavior is
changing for S+. This change adds the value reflecting the previous
default to the manifest.

Bug: 150232615
Test: TH
Change-Id: Ie0b74f7a040eb06335f11f72d2ea08513f663f3f

lowpan/tests/AndroidManifest.xml

@@ -22,7 +22,8 @@
     <application>
         <uses-library android:name="android.test.runner" />
         <activity android:label="LowpanTestDummyLabel"
-                  android:name="LowpanTestDummyName">
+                  android:name="LowpanTestDummyName"
+                  android:exported="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER"/>