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/ISocketKeepaliveCallback.aidl b/framework/src/android/net/ISocketKeepaliveCallback.aidl
index 020fbca..1240e37 100644
--- a/framework/src/android/net/ISocketKeepaliveCallback.aidl
+++ b/framework/src/android/net/ISocketKeepaliveCallback.aidl
@@ -24,7 +24,7 @@
 oneway interface ISocketKeepaliveCallback
 {
     /** The keepalive was successfully started. */
-    void onStarted(int slot);
+    void onStarted();
     /** The keepalive was successfully stopped. */
     void onStopped();
     /** The keepalive was stopped because of an error. */