Add config to only allow auto select of networks

Make it possible for carriers to prevent users from
doing a manual search of networks when in the home network.
This affects Advanced Networks Settings when the user
is not roaming.

This is sometimes called "Permanent automatic mode".

Test: Add an entry in vendor.xml
Bug: 70499144
Change-Id: I9fe91a8510683e4bb3d51efb168c0d159dbb4591