Fix SocketKeepalive APIs which do not meet API review requirement

Per API review, change the use of FileDescriptor to
ParcelFileDescriptor.
This change also fix nullability according to API review
feedbacks.

Fix: 126698610
Fix: 126699425
Fix: 126699232
Fix: 126700278

Test: 1. m -j
      2. atest FrameworksNetTests --generate-new-metrics 50
      3. m -j doc-comment-check-docs
Change-Id: I19476c50dd1ca290bf3f41973829da2bd229796a
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index 9487faf..a2c5655 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -988,7 +988,7 @@
 
         mUserManager = (UserManager) context.getSystemService(Context.USER_SERVICE);
 
-        mKeepaliveTracker = new KeepaliveTracker(mHandler);
+        mKeepaliveTracker = new KeepaliveTracker(mContext, mHandler);
         mNotifier = new NetworkNotificationManager(mContext, mTelephonyManager,
                 mContext.getSystemService(NotificationManager.class));
 
@@ -6700,7 +6700,7 @@
             ISocketKeepaliveCallback cb, String srcAddr, int srcPort, String dstAddr) {
         enforceKeepalivePermission();
         mKeepaliveTracker.startNattKeepalive(
-                getNetworkAgentInfoForNetwork(network),
+                getNetworkAgentInfoForNetwork(network), null /* fd */,
                 intervalSeconds, cb,
                 srcAddr, srcPort, dstAddr, NattSocketKeepalive.NATT_PORT);
     }
@@ -6709,7 +6709,6 @@
     public void startNattKeepaliveWithFd(Network network, FileDescriptor fd, int resourceId,
             int intervalSeconds, ISocketKeepaliveCallback cb, String srcAddr,
             String dstAddr) {
-        enforceKeepalivePermission();
         mKeepaliveTracker.startNattKeepalive(
                 getNetworkAgentInfoForNetwork(network), fd, resourceId,
                 intervalSeconds, cb,