overlay: Change vvm_type_vvm3_mvno to vvm_type_vvm3

* Google Dialer, where these values have been extracted from, apparently
  does use that type, but our Dialer doesn't support it at all
* Change it to the one we support and hope more users can now use
  VisualVoiceMail

Co-authored-by: Joel Beckmeyer <jbeckmeyer@cedarville.edu>
Change-Id: I7e602fc9c591620b5306c187cde11afac2fd697f