[strongSwan] Can strongswan work with ip port forwarding and not NAT

[Tobias Brunner]

Hi Christopher,

> Jul  8 11:47:06 localhost charon: 04[CFG]   left=41.60.182.160

You shouldn't set `left` to the public IP address of the NAT, the host
won't be able to send messages from it:

> Jul  8 11:47:11 localhost charon: 03[NET] sending packet: from
> 41.60.182.160[500] to 185.3.95.94[500]
> Jul  8 11:47:11 localhost charon: 03[NET] error writing to socket:
> Invalid argument

If you don't specify `left` it will be determined automatically.

Regards,
Tobias