Use the binder to identify keepalive in IConnectivityManager

This is much simpler and less error-prone, as well as less
subject to race conditions.

It also allows for cleaning up some TODOs.

Test: FrameworksNetTests
      CtsNetTestCases
Bug: 267116236
Change-Id: I470c709446946ef35a0324427defe2f58b434339
diff --git a/framework/src/android/net/IConnectivityManager.aidl b/framework/src/android/net/IConnectivityManager.aidl
index 7db231e..acbc31e 100644
--- a/framework/src/android/net/IConnectivityManager.aidl
+++ b/framework/src/android/net/IConnectivityManager.aidl
@@ -193,7 +193,7 @@
     void startTcpKeepalive(in Network network, in ParcelFileDescriptor pfd, int intervalSeconds,
             in ISocketKeepaliveCallback cb);
 
-    void stopKeepalive(in Network network, int slot);
+    void stopKeepalive(in ISocketKeepaliveCallback cb);
 
     String getCaptivePortalServerUrl();