Fix targetSdkVersion for NetworkStack

targetSdkVersion was set to 28 in aosp/916713, however this was broken
by the manifest refactor in aosp/923338: the targetSdk is not preserved
in the manifest merge.

Test: aapt dump badging shows targetSdkVersion 28
Change-Id: I7d06b141856e96ef011db32094bfc62a8cd1b350
diff --git a/AndroidManifest_InProcess.xml b/AndroidManifest_InProcess.xml
index 48fcecd..275cd02 100644
--- a/AndroidManifest_InProcess.xml
+++ b/AndroidManifest_InProcess.xml
@@ -20,6 +20,7 @@
           package="com.android.networkstack.inprocess"
           android:sharedUserId="android.uid.system"
           android:process="system">
+    <uses-sdk android:minSdkVersion="28" android:targetSdkVersion="28" />
     <application>
         <service android:name="com.android.server.NetworkStackService" android:process="system">
             <intent-filter>
@@ -27,4 +28,4 @@
             </intent-filter>
         </service>
     </application>
-</manifest>
\ No newline at end of file
+</manifest>