Conditionally include VCN in Tethering module

When the build system flag RELEASE_MOVE_VCN_TO_MAINLINE is true,
VCN framework lib will be included in the tethering boot classpath
fragment and the VCN service lib will be included in the
service-connectivity.jar

Bug: 375213246
Test: flag enabled: VCN libs are in the tethering module
      flag disabled: VCN libs are in the platform
Flag: RELEASE_MOVE_VCN_TO_MAINLINE
Change-Id: If0239eb1684b861b63794762915dab0d62379885
diff --git a/Tethering/apex/Android.bp b/Tethering/apex/Android.bp
index 0c05354..19dd492 100644
--- a/Tethering/apex/Android.bp
+++ b/Tethering/apex/Android.bp
@@ -155,7 +155,10 @@
         "framework-connectivity",
         "framework-connectivity-t",
         "framework-tethering",
-    ],
+    ] + select(release_flag("RELEASE_MOVE_VCN_TO_MAINLINE"), {
+        true: ["framework-connectivity-b"],
+        default: [],
+    }),
     apex_available: ["com.android.tethering"],
 
     // The bootclasspath_fragments that provide APIs on which this depends.
@@ -195,6 +198,7 @@
             "android.net.http",
             "android.net.netstats",
             "android.net.util",
+            "android.net.vcn",
         ],
 
         // The following packages and all their subpackages currently only