[Tether07] Migrate Tethering into module

Now tethering would be run in dedicated service.
TetheringManager is the interface used to communicate with
TetheringService. The new call flow would be: ConnectivityManager
-> ConnectivityService -> TetheringManager -> TetheringService.
Note: the return value of #tether(), #untether() and #setUsbTethering()
APIs would always be no error. Client can use #getLastTetherError()
or #getTetheredIfaces or listen tether state change to check
status of corresponding interface.

Bug: 136040414
Bug: 144742179
Test: -build, flash, boot
      -atest TetheringTests
      -atest FrameworksNetTests

Change-Id: I7e78c0e0a3e70f940a749ba2a39ece7c7ec5b9b3

tests/net/java/com/android/server/ConnectivityServiceTest.java

@@ -163,6 +163,7 @@ import android.net.ProxyInfo;
 import android.net.ResolverParamsParcel;
 import android.net.RouteInfo;
 import android.net.SocketKeepalive;
+import android.net.TetheringManager;
 import android.net.UidRange;
 import android.net.metrics.IpConnectivityLog;
 import android.net.shared.NetworkMonitorUtils;
@@ -210,7 +211,6 @@ import com.android.server.connectivity.MockableSystemProperties;
 import com.android.server.connectivity.Nat464Xlat;
 import com.android.server.connectivity.NetworkNotificationManager.NotificationType;
 import com.android.server.connectivity.ProxyTracker;
-import com.android.server.connectivity.Tethering;
 import com.android.server.connectivity.Vpn;
 import com.android.server.net.NetworkPinner;
 import com.android.server.net.NetworkPolicyManagerInternal;
@@ -1130,7 +1130,7 @@ public class ConnectivityServiceTest {
         doReturn(new TestNetIdManager()).when(deps).makeNetIdManager();
         doReturn(mNetworkStack).when(deps).getNetworkStack();
         doReturn(systemProperties).when(deps).getSystemProperties();
-        doReturn(mock(Tethering.class)).when(deps).makeTethering(any(), any(), any(), any(), any());
+        doReturn(mock(TetheringManager.class)).when(deps).getTetheringManager();
         doReturn(mock(ProxyTracker.class)).when(deps).makeProxyTracker(any(), any());
         doReturn(mMetricsService).when(deps).getMetricsLogger();
         doReturn(true).when(deps).queryUserAccess(anyInt(), anyInt());