Avoid synchronization state resets.
    
    Going back to sync_init state is a bad idea because it prevents
    update_*() functions from writting to journal. As a result, zone
    journals were missing changes done during resynchronization, i.e. the
    journal was corrupted and unusable for IXFR and DNSSEC in-line signing.
    
    https://fedorahosted.org/bind-dyndb-ldap/ticket/128