Adds necessary permissions to system apis

adds privileged permission for getCaptivePortalServerUrl
adds tether privileged permission for
startTethering,isTetheringSupported

bug:62348162

Test: make and manual testing
Change-Id: I8eb8e3c9dcd7201abe9ea303ee57fe99073d67eb
diff --git a/core/java/android/net/IConnectivityManager.aidl b/core/java/android/net/IConnectivityManager.aidl
index 27729dc..14cee36 100644
--- a/core/java/android/net/IConnectivityManager.aidl
+++ b/core/java/android/net/IConnectivityManager.aidl
@@ -75,7 +75,7 @@
 
     int getLastTetherError(String iface);
 
-    boolean isTetheringSupported();
+    boolean isTetheringSupported(String callerPkg);
 
     void startTethering(int type, in ResultReceiver receiver, boolean showProvisioningUi,
             String callerPkg);