Do nothing in ifup-extra

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Backup iptables, arptables, ebtables commands

For each interface create a file named e.g., tap1 under
/var/lib/snf-network/. This file will include all important
variables related to the interface (INSTANCE, IP, EUI64, etc.) and
then all iptables, arptables and ebtables commands that snf-network
has invoked while configuring it. This can be helpful for admins
while reloading ferm rules or for debugging purposes.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Use env var for state dir

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Execute command after logging it in state dir

This was forgotten when log helper function was introduced.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Introduce log and save functions

The save() function is used in order to save and backup
iptables/arptables/ebtables commands related to each interface.

The log() function is a wrapper of snf-network-log script.

Do not use a default variable for the log script. This could
cause a fork bomb if the admin forgot to define it.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Add doc section for /etc/default/snf-network

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>