d/rules: fix perms of files under /etc/nftables

Lintian complains about the permission of files under /etc/nftables.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>
d/rules: disable silent rules

Disable silent rules, so build is verbose and the Debian build services
can scan the logs.

Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>