Update TCP buffer size when switching network type

Import of non-merging change 41612 from AOSP

When PDP connects in GSM network, the TCP buffer window size is
set to max 8760. If the phone swicthes to UMTS, the TCP buffer
size is not updated to UMTS, i.e. GPRS buffer size is still
used with limited data transfer spead as a result.
This fix makes sure the TCP buffer size is updated when
switching network type.

Change-Id: Ic44a557677ffe629e83ce1f522a9f058bee6e7b2

Author: Robert Greenwalt

core/java/android/net/MobileDataStateTracker.java

@@ -184,8 +184,17 @@ public void onReceive(Context context, Intent intent) {
                 if (!TextUtils.equals(apnType, mApnType)) {
                     return;
                 }
-                mNetworkInfo.setSubtype(TelephonyManager.getDefault().getNetworkType(),
-                        TelephonyManager.getDefault().getNetworkTypeName());
+
+                int oldSubtype = mNetworkInfo.getSubtype();
+                int newSubType = TelephonyManager.getDefault().getNetworkType();
+                String subTypeName = TelephonyManager.getDefault().getNetworkTypeName();
+                mNetworkInfo.setSubtype(newSubType, subTypeName);
+                if (newSubType != oldSubtype && mNetworkInfo.isConnected()) {
+                    Message msg = mTarget.obtainMessage(EVENT_NETWORK_SUBTYPE_CHANGED,
+                                                        oldSubtype, 0, mNetworkInfo);
+                    msg.sendToTarget();
+                }
+
                 PhoneConstants.DataState state = Enum.valueOf(PhoneConstants.DataState.class,
                         intent.getStringExtra(PhoneConstants.STATE_KEY));
                 String reason = intent.getStringExtra(PhoneConstants.STATE_CHANGE_REASON_KEY);

core/java/android/net/NetworkStateTracker.java

@@ -62,6 +62,12 @@ public interface NetworkStateTracker {
      */
     public static final int EVENT_RESTORE_DEFAULT_NETWORK = 6;
 
+    /**
+     * msg.what = EVENT_NETWORK_SUBTYPE_CHANGED
+     * msg.obj = NetworkInfo object
+     */
+    public static final int EVENT_NETWORK_SUBTYPE_CHANGED = 7;
+
     /**
      * -------------------------------------------------------------
      * Control Interface

services/java/com/android/server/ConnectivityService.java

@@ -2592,6 +2592,11 @@ public void handleMessage(Message msg) {
                     //       @see bug/4455071
                     handleConnectivityChange(info.getType(), false);
                     break;
+                case NetworkStateTracker.EVENT_NETWORK_SUBTYPE_CHANGED:
+                    info = (NetworkInfo) msg.obj;
+                    type = info.getType();
+                    updateNetworkSettings(mNetTrackers[type]);
+                    break;
             }
         }
     }