DO NOT MERGE: Add stub class and filegroup for Ethernet service.

Add stub classes EthernetService, EthernetServiceImpl and build stubs
for ethernet service updatable resource, which are required to ensure
ConnectivityServiceInitializer can build in the sc-mainline-prod.

Test: m service-connectivity
Test: cherry-pick the CL on p/m/Connectivity of ethernet-mainline topic
      and m com.android.tethering
Ignore-AOSP-First: needed in sc-mainline-prod only
Change-Id: I8a9e82250df61f1d47a3e7f5b3609cf459aeffb3
diff --git a/buildstubs-t/Android.bp b/buildstubs-t/Android.bp
index 385abc6..9ca3fd2 100644
--- a/buildstubs-t/Android.bp
+++ b/buildstubs-t/Android.bp
@@ -38,6 +38,11 @@
 }
 
 filegroup {
+    name: "ethernet-service-updatable-sources",
+    srcs: [],
+}
+
+filegroup {
     name: "services.connectivity-netstats-jni-sources",
     srcs: [
         "stubs-src-jni/mock_com_android_server_net_NetworkStatsFactory.cpp",