Call ConnectivitySettingsUtils to set/get private DNS related settings

ConnectivitySettingsManager and CtsNetUtils are doing the same
thing to set/get private DNS related settings.
To prevent making the duplication code in two places, move the
body to frameworks/libs/net and call it.

Bug: 185311744
Test: atest CtsNetTestCases CtsNetTestCasesLatestSdk
Change-Id: I3272c825b86ec30c3d0bf4097088c653e668461b
diff --git a/tests/cts/net/util/Android.bp b/tests/cts/net/util/Android.bp
index b5f1208..fffd30f 100644
--- a/tests/cts/net/util/Android.bp
+++ b/tests/cts/net/util/Android.bp
@@ -27,5 +27,6 @@
         "junit",
         "net-tests-utils",
         "modules-utils-build",
+        "net-utils-framework-common",
     ],
 }