Handle comma-separated list of remote networks when making vpn_networks table

If remote_networks for an OpenVPN instance is a list of more than 1 network then none of the networks gets added to the vpn_networks table. The code simply did not address this new comma-separated list feature. Now it does, and the vpn_networks table contains all the remote networks listed.
Related to forum thread: http://forum.pfsense.org/index.php/topic,66776.msg377169.html#msg377169
and bug report #3309 - but from the bug report, there might be some other issue to be addressed also.