strongswan: Create firewall rules for outgoing IPsec traffic as well

strongswan: Create firewall rules for outgoing IPsec traffic as well

This will avoid outgoing IPsec traffic being dropped by IPFire itself,
if the default firewall behavior for outgoing traffic is set to
"blocked", and no appropriate rules have been manually configured in the
web interface.

To ensure configured IPsec tunnels will always work flawlessly,
regardless of the firewall default policy and any manually created
firewall rules, create and delete outgoing iptables rules accordingly
when bringing an IPsec connection up or down.

Tested-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>