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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>