Added ability to optionally configure NAT source address

[coofercat]

A very simple change to optionally be able to configure in the NAT source address. This becomes important if your server has multiple network devices and the network(s) you want them to be able to access aren't on the default interface.

In my case, my openvpn server has a public address on the default interface (ens3) and a private network on the secondary (ens4). Since I want to provide access to the private network, I need to be able to NAT to the address on the ens4 interface. This can be configured in easily, perhaps in a group_vars/vpn_servers.yml:

openvpn_lan_source_ip: "{{ ansible_ens4.ipv4.address }}"

Please note: the default behaviour is the original one (ie. use the ansible_default_ipv4 address).

[coofercat]

Very good point - and better style than my (rather hurried) change. Updated as requested.