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

framework/src/android/net/TcpSocketKeepalive.java

@@ -69,9 +69,7 @@ public final class TcpSocketKeepalive extends SocketKeepalive {
     protected void stopImpl() {
         mExecutor.execute(() -> {
             try {
-                if (mSlot != null) {
-                    mService.stopKeepalive(mNetwork, mSlot);
-                }
+                mService.stopKeepalive(mCallback);
             } catch (RemoteException e) {
                 Log.e(TAG, "Error stopping packet keepalive: ", e);
                 throw e.rethrowFromSystemServer();