Migrate Tethering util functions to CtsTetheringUtils

Bug: 166057846
Bug: 170265597
Test: atest MtsTetheringTest
      atest CtsTetheringTest
Change-Id: I59d529cb50b4b6cdafc6be78ad61a55ee1be0404
diff --git a/tests/cts/net/util/Android.bp b/tests/cts/net/util/Android.bp
index 1f94613..c36d976 100644
--- a/tests/cts/net/util/Android.bp
+++ b/tests/cts/net/util/Android.bp
@@ -21,5 +21,6 @@
     static_libs: [
         "compatibility-device-util-axt",
         "junit",
+        "net-tests-utils",
     ],
 }
\ No newline at end of file