Change Tethering package name

Tethering apex module is renmae from com.android.tethering.aepx to
com.android.tethering. Renmae tethering apex file context accordingly.
Also add filegroup for tethering apex.

Bug: 146471733
Test: build, flash, boot
      atest TetheringTests
      atest CtsTetheringTest

Change-Id: I41ec17604067c684123085841182408c4e315ec2
Merged-In: I41ec17604067c684123085841182408c4e315ec2

apex/Android.bp

@@ -152,3 +152,10 @@ filegroup {
     "com.android.wifi-file_contexts",
   ],
 }
+
+filegroup {
+  name: "com.android.tethering-file_contexts",
+  srcs: [
+    "com.android.tethering-file_contexts",
+  ],
+}