python-netifaces: update to reflect upstream changes
    
    python-netifaces now provides IPv6 netmask in format mask/prefix. It
    breaks freeipa as it is unexpected format for python-netaddr. We must
    split netmask and provide only prefix for netaddr.
    
    https://pagure.io/freeipa/issue/7021
    
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>