Make READ_VOICEMAIL/WRITE_VOICEMAIL system permissions

Bug: 18020724
Change-Id: I5a0e5ef8a1e40ee23f4b132f5877b63a738e776e
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 0767dbb4..f35b2e8 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -679,14 +679,14 @@
     <!-- Allows an application to modify and remove existing voicemails in the system -->
     <permission android:name="com.android.voicemail.permission.WRITE_VOICEMAIL"
         android:permissionGroup="android.permission-group.VOICEMAIL"
-        android:protectionLevel="dangerous"
+        android:protectionLevel="system|signature"
         android:label="@string/permlab_writeVoicemail"
         android:description="@string/permdesc_writeVoicemail" />
 
     <!-- Allows an application to read voicemails in the system. -->
     <permission android:name="com.android.voicemail.permission.READ_VOICEMAIL"
         android:permissionGroup="android.permission-group.VOICEMAIL"
-        android:protectionLevel="dangerous"
+        android:protectionLevel="system|signature"
         android:label="@string/permlab_readVoicemail"
         android:description="@string/permdesc_readVoicemail" />