feat(vpn): auto detection of IPv6 support

- `OPENVPN_IPV6` removed
- Affects OpenVPN
- Use the same mechanism for OpenVPN and Wireguard
- Check only once at program start since this is unlikely to change at runtime
- Log if IPv6 is supported
- Remove `IPv6` boolean from settings structs
- Move IPv6 detection as a method on NetLinker

internal/provider/vpnsecure/openvpnconf.go

@@ -8,7 +8,7 @@ import (
 )
 
 func (p *Provider) OpenVPNConfig(connection models.Connection,
-	settings settings.OpenVPN) (lines []string) {
+	settings settings.OpenVPN, ipv6Supported bool) (lines []string) {
 	//nolint:gomnd
 	providerSettings := utils.OpenVPNProviderSettings{
 		RemoteCertTLS: true,
@@ -22,5 +22,5 @@ func (p *Provider) OpenVPNConfig(connection models.Connection,
 		},
 		CA: "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", //nolint:lll
 	}
-	return utils.OpenVPNConfig(providerSettings, connection, settings)
+	return utils.OpenVPNConfig(providerSettings, connection, settings, ipv6Supported)
 }