Update connected clients when a downstream disappears.

Otherwise, if another downstream of the same type reappears, the
code would fire a callback with the previous list of clients.

Bug: 150644681
Test: atest TetheringIntegrationTests:EthernetTetheringTest --rerun-until-failure 100
Change-Id: I6b34ea747ae1831001077f44879bb6828dcecc96
Merged-In: I6b34ea747ae1831001077f44879bb6828dcecc96
(cherry picked from commit 3984360f642ddd5820ced5a6935e37a8ae0d9d76)
diff --git a/Tethering/src/com/android/server/connectivity/tethering/Tethering.java b/Tethering/src/com/android/server/connectivity/tethering/Tethering.java
index 3624dc7..c84892d 100644
--- a/Tethering/src/com/android/server/connectivity/tethering/Tethering.java
+++ b/Tethering/src/com/android/server/connectivity/tethering/Tethering.java
@@ -433,9 +433,7 @@
         // Called by wifi when the number of soft AP clients changed.
         @Override
         public void onConnectedClientsChanged(final List<WifiClient> clients) {
-            if (mConnectedClientsTracker.updateConnectedClients(mForwardedDownstreams, clients)) {
-                reportTetherClientsChanged(mConnectedClientsTracker.getLastTetheredClients());
-            }
+            updateConnectedClients(clients);
         }
     }
 
@@ -1575,6 +1573,7 @@
             mIPv6TetheringCoordinator.removeActiveDownstream(who);
             mOffload.excludeDownstreamInterface(who.interfaceName());
             mForwardedDownstreams.remove(who);
+            updateConnectedClients(null /* wifiClients */);
 
             // If this is a Wi-Fi interface, tell WifiManager of any errors
             // or the inactive serving state.
@@ -2157,6 +2156,12 @@
         return false;
     }
 
+    private void updateConnectedClients(final List<WifiClient> wifiClients) {
+        if (mConnectedClientsTracker.updateConnectedClients(mForwardedDownstreams, wifiClients)) {
+            reportTetherClientsChanged(mConnectedClientsTracker.getLastTetheredClients());
+        }
+    }
+
     private IpServer.Callback makeControlCallback() {
         return new IpServer.Callback() {
             @Override
@@ -2171,10 +2176,7 @@
 
             @Override
             public void dhcpLeasesChanged() {
-                if (mConnectedClientsTracker.updateConnectedClients(
-                        mForwardedDownstreams, null /* wifiClients */)) {
-                    reportTetherClientsChanged(mConnectedClientsTracker.getLastTetheredClients());
-                }
+                updateConnectedClients(null /* wifiClients */);
             }
         };
     }