avoid emitting VPN traffic to the internet if the IPS crashed

avoid emitting VPN traffic to the internet if the IPS crashed

Due to strange NFQUEUE behaviour, traffic to remote VPN (IPsec or
OpenVPN) destinations was emitted to the internet (ppp0 or red0
interface) directly if the IPS was enabled but crashed during operation.

This patch places the IPSECBLOCK and OVPNBLOCK chains before the
ones responsible for forwarding traffic into the IPS.

Thanks to Michael for his debugging effort.

Partially fixes #12257

Cc: Michael Tremer <michael.tremer@ipfire.org>
Cc: Stefan Schantl <stefan.schantl@ipfire.org>
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Acked-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>