Setting MTU size for specific network.

Able to config network specific MTU size. Normally, the default size of MTU is 1500.
 US - ATT 1410, TMUS 1440, SPRINT 1422
 KR - SKT 1440, KT 1450, LGU+ 1428
 JP - KDDI 1420, SoftBank 1340
 CA - RGS 1430, FIDO 1430, MTS 1430, BELL 1358, SaskTel 1358
 AU - TEL 1400

Bug: 10195070
Change-Id: Ie18650b37a3d44af944f2dae4aa97c04fb12cd5e

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

@@ -2299,6 +2299,7 @@ public class ConnectivityService extends IConnectivityManager.Stub {
         }
         thisNet.setTeardownRequested(false);
         updateNetworkSettings(thisNet);
+        updateMtuSizeSettings(thisNet);
         handleConnectivityChange(newNetType, false);
         sendConnectedBroadcastDelayed(info, getConnectivityChangeDelay());
 
@@ -2636,6 +2637,26 @@ public class ConnectivityService extends IConnectivityManager.Stub {
         return routesChanged;
     }
 
+   /**
+     * Reads the network specific MTU size from reources.
+     * and set it on it's iface.
+     */
+   private void updateMtuSizeSettings(NetworkStateTracker nt) {
+       final String iface = nt.getLinkProperties().getInterfaceName();
+       final int mtu = nt.getLinkProperties().getMtu();
+
+       if (mtu < 68 || mtu > 10000) {
+           loge("Unexpected mtu value: " + nt);
+           return;
+       }
+
+       try {
+           if (VDBG) log("Setting MTU size: " + iface + ", " + mtu);
+           mNetd.setMtu(iface, mtu);
+       } catch (Exception e) {
+           Slog.e(TAG, "exception in setMtu()" + e);
+       }
+   }
 
     /**
      * Reads the network specific TCP buffer sizes from SystemProperties
@@ -4774,4 +4795,3 @@ public class ConnectivityService extends IConnectivityManager.Stub {
         mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, wakeupTime, intent);
     }
 }
-