Add lockdownEnabled parameter to always-on VPN API

Allows callers to opt-out of blockading network traffic during boot and
on VPN app failure.

Bug: 26694104
Change-Id: Ic2c25b79d8a17917025eb37be7de929fe156e2a3

src/com/android/settings/vpn2/ConfigDialogFragment.java

@@ -153,7 +153,8 @@ public class ConfigDialogFragment extends DialogFragment implements
             }
 
             final ConnectivityManager conn = ConnectivityManager.from(getActivity());
-            conn.setAlwaysOnVpnPackageForUser(UserHandle.myUserId(), null);
+            conn.setAlwaysOnVpnPackageForUser(UserHandle.myUserId(), null,
+                    /* lockdownEnabled */ false);
             VpnUtils.setLockdownVpn(getContext(), profile.key);
         } else {
             // update only if lockdown vpn has been changed