Partly revert commit 4c45712f
Merge pull request #311 from bcyrill/ipv6_newwanip

Partly revert commit 4c45712f
Fix typo
Retain user configured values for all fields when a validation error occours. It should fix #2745
Unbreak selecting "any" for OpenVPN client/server interface.
While I'm here, allow selecting "Localhost" as an OpenVPN interface.