No-op Refactoring of startTrackDefaultNetwork

While the actual part that track default request is inside
UpstreamNetworkMonitor, instead of passing it from Tethering,
move it into counter-part CL and use it from
UpstreamNetworkMonitor.

Since the current code is replaced by registerSystemDefaultCallback
in Android S, implement it inside the api30 shim implementation
to provide an unified interface to tethering.

Test: atest TetheringCoverageTests
Bug: 185952829
Change-Id: Iaf21b6b662aa6aba79c2b75379128b8523f81f02
diff --git a/Tethering/Android.bp b/Tethering/Android.bp
index 4eafc2a..79c2b9d 100644
--- a/Tethering/Android.bp
+++ b/Tethering/Android.bp
@@ -30,6 +30,7 @@
         ":services-tethering-shared-srcs",
     ],
     static_libs: [
+        "NetworkStackApiStableShims",
         "androidx.annotation_annotation",
         "modules-utils-build",
         "netlink-client",