Settings (and general) restore fixes

Pro tem, we ignore wifi configuration data when restoring system settings.
This is not ideal, but it *does* mean we do not bounce wifi off and on
again during the extended restore process, which in turn means we don't
interfere with things like the Play Store's download of applications.
We do continue to back up wifi configuration, and will start using that
data again when the new implementation that restores AP configurations
without having to bounce wifi comes to pass.

Also, this CL fixes a longstanding bug in BackupDataInput.skipEntityData()
that was being reproduced reliably once settings restore was skipping
the wifi-related entities in the restore stream.

Bug 7249405

Change-Id: I61520a9a116b66ebdf95734d09d9afd46406df01