Issue title: Split VPN
 Issue body: This is more of a question that an issue. The vpn works great if I select to pass all traffic to it. I was curious if there is something I can set on the server side to only pass a couple /32s over the VPN. Any help or direction would be much appreciated. Thanks.
 Comments: 
 Comment 0: @jsindy What you need is called "Split Tunneling". It is controlled by the "leftsubnet" directive in "/etc/ipsec.conf". Here are some references [1] [2] [3]. Search for "split tunneling" on these pages. When finished making changes, restart the IPsec service with "service ipsec restart".

I don't have much experience on the split tunneling though. Further questions can be asked on the Libreswan or Strongswan mailing lists [4] [5], on which many VPN experts could help. Good luck!

[1] https://wiki.strongswan.org/projects/strongswan/wiki/ForwardingAndSplitTunneling   
[2] https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Security_Guide/sec-Securing_Virtual_Private_Networks.html   
[3] https://libreswan.org/man/ipsec.conf.5.html   
[4] https://lists.libreswan.org/mailman/listinfo/swan   
[5] https://lists.strongswan.org/mailman/listinfo/users
 Comment 1: Thanks a million @hwdsl2 !
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