spec: Fix permissions of nwfilter XMLs

spec: Fix permissions of nwfilter XMLs

The nwfilter XML files stored in /etc/libvirt/nwfilter are copied in a
%post scriptlet from /usr/share/libvirt/nwfilter/*.xml. While the files
in /usr/share are created with mode 0644, libvirt creates the files in
/etc/libvirt/nwfilter with mode 0600. Since 0600 is also stored in the
RPM database, we need to chmod the files copied from /usr/share to make
sure RPM verification does not complain about changed permissions.

https://bugzilla.redhat.com/show_bug.cgi?id=1628475

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>