Inappropriate node name in VTN configuration file.

Virtual interface configuration is saved in XML file like this:

<vinterfaces>
<interfaces>
<name>if_1</name>
<enabled>true</enabled>
</interfaces>
<interfaces>
<name>if_2</name>
<enabled>false</enabled>
</interfaces>
</vinterfaces>

<interfaces> is inappropriate for virtual interface configuration.
<vinterface> should be used instead.