LinkProperties function to compare provisioning and remove DNS servers

Adds:
    - enum ProvisioningChange
    - LinkProperties#compareProvisioning()
          return a ProvisioningChange value describing the delta in
          provisioning between two LinkProperties objects
    - LinkProperties#removeDnsServer()
    - make "@hide public" isIPv4Provisioned() and isIPv6Provisioned()

Bug: 18581716
Change-Id: I3df90b2b89617f693346f2dbe72e77c88ce91ffd