addrconf: avoid unwanted updates, update flag fixes

    - Splitted addrconf updater type and update bitmap
    - Defined the update flags in the schema and fixed
      to initialize to all known flags instead to ~0.
    - Read several dhclient variables from suse ifcfg
      config such as update hostname (bnc#865325) and
      also diverse timing variables (not all used yet).
    - Fixed extensions/hostname to verify its state and
      drop obsolete state to allow to switch to use a
      hostname from different lease (reconfiguration).